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    #[cfg(feature = "yaml")]
    use std::collections::BTreeMap;
    use std::rc::Rc;

    #[cfg(feature = "yaml")]
    use yaml_rust::Yaml;
    use vec_map::VecMap;

    use usage_parser::UsageParser;
    use args::settings::{ArgSettings, ArgFlags};

    /// The abstract representation of a command line argument. Used to set all the options and
    /// relationships that define a valid argument for the program.
    ///
    /// There are two methods for constructing `Arg`s, using the builder pattern and setting options
    /// manually, or using a usage string which is far less verbose but has fewer options. You can also
    /// use a combination of the two methods to achieve the best of both worlds.
    ///
    /// # Examples
    ///
    /// ```rust
    /// # use clap::Arg;
    /// // Using the traditional builder pattern and setting each option manually
    /// let cfg = Arg::with_name("config")
    ///       .short("c")
    ///       .long("config")
    ///       .takes_value(true)
    ///       .value_name("FILE")
    ///       .help("Provides a config file to myprog");
    /// // Using a usage string (setting a similar argument to the one above)
    /// let input = Arg::from_usage("-i, --input=[FILE] 'Provides an input file to the program'");
    /// ```
    #[allow(missing_debug_implementations)]
    pub struct Arg<'a, 'b> where 'a: 'b {
        #[doc(hidden)]
        pub name: &'a str,
        #[doc(hidden)]
        pub short: Option<char>,
        #[doc(hidden)]
        pub long: Option<&'b str>,
        #[doc(hidden)]
        pub help: Option<&'b str>,
        #[doc(hidden)]
        pub index: Option<u64>,
        #[doc(hidden)]
        pub blacklist: Option<Vec<&'a str>>,
        #[doc(hidden)]
        pub possible_vals: Option<Vec<&'b str>>,
        #[doc(hidden)]
        pub requires: Option<Vec<&'a str>>,
        #[doc(hidden)]
        pub group: Option<&'a str>,
        #[doc(hidden)]
        pub val_names: Option<VecMap<&'b str>>,
        #[doc(hidden)]
        pub num_vals: Option<u64>,
        #[doc(hidden)]
        pub max_vals: Option<u64>,
        #[doc(hidden)]
        pub min_vals: Option<u64>,
        #[doc(hidden)]
        pub validator: Option<Rc<Fn(String) -> Result<(), String>>>,
        #[doc(hidden)]
        pub overrides: Option<Vec<&'a str>>,
        #[doc(hidden)]
        pub settings: ArgFlags,
        #[doc(hidden)]
        pub val_delim: Option<char>,
        #[doc(hidden)]
        pub default_val: Option<&'a str>,
        #[doc(hidden)]
        pub disp_ord: usize,
        #[doc(hidden)]
        pub r_unless: Option<Vec<&'a str>>,
    }

    impl<'a, 'b> Default for Arg<'a, 'b> {
        fn default() -> Self {
            Arg {
                name: "".as_ref(),
                short: None,
                long: None,
                help: None,
                index: None,
                blacklist: None,
                possible_vals: None,
                requires: None,
                group: None,
                val_names: None,
                num_vals: None,
                max_vals: None,
                min_vals: None,
                validator: None,
                overrides: None,
                settings: ArgFlags::new(),
                val_delim: Some(','),
                default_val: None,
                disp_ord: 999,
                r_unless: None,
            }
        }
    }

    impl<'a, 'b> Arg<'a, 'b> {
        /// Creates a new instance of `Arg` using a unique string name. The name will be used to get
        /// information about whether or not the argument was used at runtime, get values, set
        /// relationships with other args, etc..
        ///
        /// **NOTE:** In the case of arguments that take values (i.e. `takes_value(true)`)
        /// and positional arguments (i.e. those without a preceding `-` or `--`) the name will also
        /// be displayed when the user prints the usage/help information of the program.
        ///
        /// # Examples
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// Arg::with_name("config")
        /// # ;
        /// ```
        pub fn with_name(n: &'a str) -> Self {
            Arg {
                name: n,
                ..Default::default()
            }
        }

        /// Creates a new instance of `Arg` from a .yml (YAML) file.
        ///
        /// # Examples
        ///
        /// ```ignore
        /// # use clap::Arg;
        /// let yml = load_yaml!("arg.yml");
        /// let arg = Arg::from_yaml(yml);
        /// ```
        #[cfg(feature = "yaml")]
        pub fn from_yaml<'y>(y: &'y BTreeMap<Yaml, Yaml>) -> Arg<'y, 'y> {
            // We WANT this to panic on error...so expect() is good.
            let name_yml = y.keys().nth(0).unwrap();
            let name_str = name_yml.as_str().unwrap();
            let mut a = Arg::with_name(name_str);
            let arg_settings = y.get(name_yml).unwrap().as_hash().unwrap();

            for (k, v) in arg_settings.iter() {
                a = match k.as_str().unwrap() {
                    "short" => a.short(v.as_str().unwrap()),
                    "long" => a.long(v.as_str().unwrap()),
                    "help" => a.help(v.as_str().unwrap()),
                    "required" => a.required(v.as_bool().unwrap()),
                    "takes_value" => a.takes_value(v.as_bool().unwrap()),
                    "index" => a.index(v.as_i64().unwrap() as u64),
                    "global" => a.global(v.as_bool().unwrap()),
                    "multiple" => a.multiple(v.as_bool().unwrap()),
                    "empty_values" => a.empty_values(v.as_bool().unwrap()),
                    "group" => a.group(v.as_str().unwrap()),
                    "number_of_values" => a.number_of_values(v.as_i64().unwrap() as u64),
                    "max_values" => a.max_values(v.as_i64().unwrap() as u64),
                    "min_values" => a.min_values(v.as_i64().unwrap() as u64),
                    "value_name" => a.value_name(v.as_str().unwrap()),
                    "use_delimiter" => a.use_delimiter(v.as_bool().unwrap()),
                    "value_delimiter" => a.value_delimiter(v.as_str().unwrap()),
                    "required_unless" => a.required_unless(v.as_str().unwrap()),
                    "display_order" => a.display_order(v.as_i64().unwrap() as usize),
                    "value_names" => {
                        for ys in v.as_vec().unwrap() {
                            if let Some(s) = ys.as_str() {
                                a = a.value_name(s);
                            }
                        }
                        a
                    }
                    "requires" => {
                        for ys in v.as_vec().unwrap() {
                            if let Some(s) = ys.as_str() {
                                a = a.requires(s);
                            }
                        }
                        a
                    }
                    "conflicts_with" => {
                        for ys in v.as_vec().unwrap() {
                            if let Some(s) = ys.as_str() {
                                a = a.conflicts_with(s);
                            }
                        }
                        a
                    }
                    "overrides_with" => {
                        for ys in v.as_vec().unwrap() {
                            if let Some(s) = ys.as_str() {
                                a = a.overrides_with(s);
                            }
                        }
                        a
                    }
                    "possible_values" => {
                        for ys in v.as_vec().unwrap() {
                            if let Some(s) = ys.as_str() {
                                a = a.possible_value(s);
                            }
                        }
                        a
                    }
                    "required_unless_one" => {
                        for ys in v.as_vec().unwrap() {
                            if let Some(s) = ys.as_str() {
                                a = a.required_unless(s);
                            }
                        }
                        a
                    }
                    "required_unless_all" => {
                        for ys in v.as_vec().unwrap() {
                            if let Some(s) = ys.as_str() {
                                a = a.required_unless(s);
                            }
                        }
                        a.setb(ArgSettings::RequiredUnlessAll);
                        a
                    }
                    s => panic!("Unknown Arg setting '{}' in YAML file for arg '{}'",
                                s,
                                name_str),
                }
            }

            a
        }

        /// Creates a new instance of `Arg` from a usage string. Allows creation of basic settings for
        /// the `Arg`. The syntax is flexible, but there are some rules to follow.
        ///
        /// **NOTE**: Not all settings may be set using the usage string method. Some properties are
        /// only available via the builder pattern.
        ///
        /// **NOTE**: Only ASCII values in `from_usage` strings are officially supported. Some UTF-8
        /// codepoints may work just fine, but this is not guaranteed.
        ///
        /// # Syntax
        ///
        /// Usage strings typically following the form:
        ///
        /// ```notrust
        /// [explicit name] [short] [long] [value names] [help string]
        /// ```
        ///
        /// This is not a hard rule as the attributes can appear in other orders. There are also
        /// several additional sigils which denote additional settings. Below are the details of each
        /// portion of the string.
        ///
        /// ### Explicit Name
        ///
        /// This is an optional field, if it's omitted the argumenet will use one of the additioinal
        /// fields as the name using the following priority order:
        ///
        ///  * Explicit Name (This always takes precedence when present)
        ///  * Long
        ///  * Short
        ///  * Value Name
        ///
        /// `clap` determines explicit names as the first string of characters between either `[]` or
        /// `<>` where `[]` has the dual notation of meaning the argument is optional, and `<>` meaning
        /// the argument is required.
        ///
        /// Explicit names may be followed by:
        ///  * The multiple denotation `...`
        ///
        /// Example explicit names as follows (`ename` for an optional argument, and `rname` for a
        /// required argument):
        ///
        /// ```notrust
        /// [ename] -s, --long 'some flag'
        /// <rname> -r, --longer 'some other flag'
        /// ```
        ///
        /// ### Short
        ///
        /// This is set by placing a single character after a leading `-`.
        ///
        /// Shorts may be followed by
        ///  * The multiple denotation `...`
        ///  * An optional comma `,` which is cosmetic only
        ///  * Value notation
        ///
        /// Example shorts are as follows (`-s`, and `-r`):
        ///
        /// ```notrust
        /// -s, --long 'some flag'
        /// <rname> -r [val], --longer 'some option'
        /// ```
        ///
        /// ### Long
        ///
        /// This is set by placing a word (no spaces) after a leading `--`.
        ///
        /// Shorts may be followed by
        ///  * The multiple denotation `...`
        ///  * Value notation
        ///
        /// Example longs are as follows (`--some`, and `--rapid`):
        ///
        /// ```notrust
        /// -s, --some 'some flag'
        /// --rapid=[FILE] 'some option'
        /// ```
        ///
        /// ### Values (Value Notation)
        ///
        /// This is set by placing a word(s) between `[]` or `<>` optionally after `=` (although this
        /// is cosmetic only and does not affect functionality). If an explicit name has **not** been
        /// set, using `<>` will denote a required argument, and `[]` will denote an optional argument
        ///
        /// Values may be followed by
        ///  * The multiple denotation `...`
        ///  * More Value notation
        ///
        /// More than one value will also implicitly set the arguments number of values, i.e. having
        /// two values, `--option [val1] [val2]` specifies that in order for option to be satisified it
        /// must receive exactly two values
        ///
        /// Example values are as follows (`FILE`, and `SPEED`):
        ///
        /// ```notrust
        /// -s, --some [FILE] 'some option'
        /// --rapid=<SPEED>... 'some required multiple option'
        /// ```
        ///
        /// ### Help String
        ///
        /// The help string is denoted between a pair of single quotes `''` and may contain any characters.
        ///
        /// Example help strings are as follows:
        ///
        /// ```notrust
        /// -s, --some [FILE] 'some option'
        /// --rapid=<SPEED>... 'some required multiple option'
        /// ```
        ///
        /// ### Additional Sigils
        ///
        /// Multiple notation `...` (three consecutive dots/periods) specifies that this argument may
        /// be used multiple times. Do not confuse multiple occurrences (`...`) with multiple values.
        /// `--option val1 val2` is a single occurrence with multiple values. `--flag --flag` is
        /// multiple occurrences (and then you can obviously have instances of both as well)
        ///
        /// # Examples
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// App::new("myprog")
        ///     .args(&[
        ///         Arg::from_usage("--config <FILE> 'a required file for the configuration and no short'"),
        ///         Arg::from_usage("-d, --debug... 'turns on debugging information and allows multiples'"),
        ///         Arg::from_usage("[input] 'an optional input file to use'")
        /// ])
        /// # ;
        /// ```
        pub fn from_usage(u: &'a str) -> Self {
            let parser = UsageParser::from_usage(u);
            parser.parse()
        }

        /// Sets the short version of the argument without the preceding `-`.
        ///
        /// By default `clap` automatically assigns `V` and `h` to display version and help information
        /// respectively. You may use `V` or `h` for your own purposes, in which case `clap` simply
        /// will not assign those to the displaying of version or help.
        ///
        /// **NOTE:** Any leading `-` characters will be stripped, and only the first
        /// non `-` character will be used as the `short` version
        ///
        /// # Examples
        ///
        /// To set `short` use a single valid UTF-8 codepoint. If you supply a leading `-` such as `-c`
        /// it will be stripped.
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// Arg::with_name("config")
        ///     .short("c")
        /// # ;
        /// ```
        ///
        /// Setting `short` allows using the argument via a single hyphen (`-`) such as `-c`
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// let m = App::new("shorttest")
        ///     .arg(Arg::with_name("config")
        ///         .short("c"))
        ///     .get_matches_from(vec![
        ///         "shorttest", "-c"
        ///     ]);
        ///
        /// assert!(m.is_present("config"));
        /// ```
        pub fn short<S: AsRef<str>>(mut self, s: S) -> Self {
            self.short = s.as_ref().trim_left_matches(|c| c == '-').chars().nth(0);
            self
        }

        /// Sets the long version of the argument without the preceding `--`.
        ///
        /// By default `clap` automatically assigns `version` and `help` to display version and help
        /// information respectively. You may use `version` or `help` for your own purposes, in which
        /// case `clap` simply will not assign those to the displaying of version or help automatically,
        /// and you will have to do so manually.
        ///
        /// **NOTE:** Any leading `-` characters will be stripped
        ///
        /// # Examples
        ///
        /// To set `long` use a word containing valid UTF-8 codepoints. If you supply a dobule leading
        /// `--` such as `--config` they will be stripped. Hyphens in the middle of the word, however,
        /// will *not* be stripped (i.e. `config-file` is allowed)
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// Arg::with_name("cfg")
        ///     .long("config")
        /// # ;
        /// ```
        ///
        /// Setting `long` allows using the argument via a double hyphen (`--`) such as `--config`
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// let m = App::new("longtest")
        ///     .arg(Arg::with_name("cfg")
        ///         .long("config"))
        ///     .get_matches_from(vec![
        ///         "shorttest", "--config"
        ///     ]);
        ///
        /// assert!(m.is_present("cfg"));
        /// ```
        pub fn long(mut self, l: &'b str) -> Self {
            self.long = Some(l.trim_left_matches(|c| c == '-'));
            self
        }

        /// Sets the help text of the argument that will be displayed to the user when they print the
        /// usage/help information.
        ///
        /// # Examples
        ///
        /// Any valid `String` slice is allowed as help (i.e. only valid UTF-8). The one exception is
        /// one wishes to include a newline in the help text. To include a newline **and** be properly
        /// aligned with all other arguments help text, it must be specified via `{n}` instead of `\n`.
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// Arg::with_name("config")
        ///     .help("The config file used by the myprog")
        /// # ;
        /// ```
        ///
        /// Setting `help` displays a short message to the side of the argument when the user passes
        /// `-h` or `--help` (by default).
        ///
        /// ```ignore
        /// # use clap::{App, Arg};
        /// let m = App::new("helptest")
        ///     .arg(Arg::with_name("cfg")
        ///         .long("config")
        ///         .help("Some help text describing the --config arg"))
        ///     .get_matches_from(vec![
        ///         "shorttest", "--help"
        ///     ]);
        ///
        /// // ...
        /// ```
        ///
        /// The above example displays
        ///
        /// ```notrust
        /// helptest
        ///
        /// USAGE:
    	///    helptest [FLAGS]
        ///
        /// FLAGS:
        ///     --config     Some help text describing the --config arg
        /// -h, --help       Prints help information
        /// -V, --version    Prints version information
        /// ```
        pub fn help(mut self, h: &'b str) -> Self {
            self.help = Some(h);
            self
        }

        /// Sets whether or not the argument is required by default. Required by default means it is
        /// required, when no other conflicting rules have been evaluated. Conflicting rules take
        /// precedence over being required. **Default:** `false`
        ///
        /// **NOTE:** Flags (i.e. not positional, or arguments that take values) cannot be required.
        ///
        /// # Examples
        ///
        /// ```rust
        /// # use clap::Arg;
        /// Arg::with_name("config")
        ///     .required(true)
        /// # ;
        /// ```
        ///
        /// Setting `required(true)` requires that the argument be used at runtime.
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// let res = App::new("longtest")
        ///     .arg(Arg::with_name("cfg")
        ///         .required(true)
        ///         .takes_value(true)
        ///         .long("config"))
        ///     .get_matches_from_safe(vec![
        ///         "shorttest", "--config", "file.conf"
        ///     ]);
        ///
        /// assert!(res.is_ok());
        /// ```
        ///
        /// Setting `required(true)` and *not* supplying that argument is an error.
        ///
        /// ```rust
        /// # use clap::{App, Arg, ErrorKind};
        /// let res = App::new("longtest")
        ///     .arg(Arg::with_name("cfg")
        ///         .required(true)
        ///         .takes_value(true)
        ///         .long("config"))
        ///     .get_matches_from_safe(vec![
        ///         "shorttest"
        ///     ]);
        ///
        /// assert!(res.is_err());
        /// assert_eq!(res.unwrap_err().kind, ErrorKind::MissingRequiredArgument);
        /// ```
        pub fn required(self, r: bool) -> Self {
            if r { self.set(ArgSettings::Required) } else { self.unset(ArgSettings::Required) }
        }

        /// Sets an arg that override this arg's required setting. (i.e. this arg will be required
        /// unless this other argument is present).
        ///
        /// **Pro Tip:** Using `Arg::required_unless` implies `Arg::required` and is therefore not
        /// mandatory to also set.
        ///
        /// # Examples
        ///
        /// ```rust
        /// # use clap::Arg;
        /// Arg::with_name("config")
        ///     .required_unless("debug")
        /// # ;
        /// ```
        ///
        /// Setting `required_unless(name)` requires that the argument be used at runtime *unless*
        /// `name` is present. In the following example, the required argument is *not* provided, but
        /// it's not an error because the `unless` arg has been supplied.
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// let res = App::new("unlesstest")
        ///     .arg(Arg::with_name("cfg")
        ///         .required_unless("dbg")
        ///         .takes_value(true)
        ///         .long("config"))
        ///     .arg(Arg::with_name("dbg")
        ///         .long("debug"))
        ///     .get_matches_from_safe(vec![
        ///         "unlesstest", "--debug"
        ///     ]);
        ///
        /// assert!(res.is_ok());
        /// ```
        ///
        /// Setting `required_unless(name)` and *not* supplying `name` or this arg is an error.
        ///
        /// ```rust
        /// # use clap::{App, Arg, ErrorKind};
        /// let res = App::new("unlesstest")
        ///     .arg(Arg::with_name("cfg")
        ///         .required_unless("dbg")
        ///         .takes_value(true)
        ///         .long("config"))
        ///     .arg(Arg::with_name("dbg")
        ///         .long("debug"))
        ///     .get_matches_from_safe(vec![
        ///         "unlesstest"
        ///     ]);
        ///
        /// assert!(res.is_err());
        /// assert_eq!(res.unwrap_err().kind, ErrorKind::MissingRequiredArgument);
        /// ```
        pub fn required_unless(mut self, name: &'a str) -> Self {
            if let Some(ref mut vec) = self.r_unless {
                vec.push(name);
            } else {
                self.r_unless = Some(vec![name]);
            }
            self.required(true)
        }

        /// Sets args that override this arg's required setting. (i.e. this arg will be required unless
        /// all these other argument are present).
        ///
        /// **NOTE:** If you wish for the this argument to only be required if *one of* these args are
        /// present see `Arg::required_unless_one`
        ///
        /// # Examples
        ///
        /// ```rust
        /// # use clap::Arg;
        /// Arg::with_name("config")
        ///     .required_unless_all(&["cfg", "dbg"])
        /// # ;
        /// ```
        ///
        /// Setting `required_unless_all(names)` requires that the argument be used at runtime *unless*
        /// *all* the args in `names` are present. In the following example, the required argument is
        /// *not* provided, but it's not an error because all the `unless` args have been supplied.
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// let res = App::new("unlessall")
        ///     .arg(Arg::with_name("cfg")
        ///         .required_unless_all(&["dbg", "infile"])
        ///         .takes_value(true)
        ///         .long("config"))
        ///     .arg(Arg::with_name("dbg")
        ///         .long("debug"))
        ///     .arg(Arg::with_name("infile")
        ///         .short("i")
        ///         .takes_value(true))
        ///     .get_matches_from_safe(vec![
        ///         "unlessall", "--debug", "-i", "file"
        ///     ]);
        ///
        /// assert!(res.is_ok());
        /// ```
        ///
        /// Setting `required_unless_all(names)` and *not* supplying *all* of `names` or this arg is an
        /// error.
        ///
        /// ```rust
        /// # use clap::{App, Arg, ErrorKind};
        /// let res = App::new("unlessall")
        ///     .arg(Arg::with_name("cfg")
        ///         .required_unless_all(&["dbg", "infile"])
        ///         .takes_value(true)
        ///         .long("config"))
        ///     .arg(Arg::with_name("dbg")
        ///         .long("debug"))
        ///     .arg(Arg::with_name("infile")
        ///         .short("i")
        ///         .takes_value(true))
        ///     .get_matches_from_safe(vec![
        ///         "unlessall"
        ///     ]);
        ///
        /// assert!(res.is_err());
        /// assert_eq!(res.unwrap_err().kind, ErrorKind::MissingRequiredArgument);
        /// ```
        pub fn required_unless_all(mut self, names: &[&'a str]) -> Self {
            if let Some(ref mut vec) = self.r_unless {
                for s in names {
                    vec.push(s);
                }
            } else {
                self.r_unless = Some(names.iter().map(|s| *s).collect::<Vec<_>>());
            }
            self.setb(ArgSettings::RequiredUnlessAll);
            self.required(true)
        }

        /// Sets args that override this arg's required setting. (i.e. this arg will be required unless
        /// *at least one of* these other argument are present).
        ///
        /// **NOTE:** If you wish for the this argument to only be required if *all of* these args are
        /// present see `Arg::required_unless_all`
        ///
        /// # Examples
        ///
        /// ```rust
        /// # use clap::Arg;
        /// Arg::with_name("config")
        ///     .required_unless_all(&["cfg", "dbg"])
        /// # ;
        /// ```
        ///
        /// Setting `required_unless_one(names)` requires that the argument be used at runtime *unless*
        /// *at least one of* the args in `names` are present. In the following example, the required
        /// argument is *not* provided, but it's not an error because one the `unless` args have been
        /// supplied.
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// let res = App::new("unlessone")
        ///     .arg(Arg::with_name("cfg")
        ///         .required_unless_one(&["dbg", "infile"])
        ///         .takes_value(true)
        ///         .long("config"))
        ///     .arg(Arg::with_name("dbg")
        ///         .long("debug"))
        ///     .arg(Arg::with_name("infile")
        ///         .short("i")
        ///         .takes_value(true))
        ///     .get_matches_from_safe(vec![
        ///         "unlessone", "--debug"
        ///     ]);
        ///
        /// assert!(res.is_ok());
        /// ```
        ///
        /// Setting `required_unless_one(names)` and *not* supplying *at least one of* `names` or this
        /// arg is an error.
        ///
        /// ```rust
        /// # use clap::{App, Arg, ErrorKind};
        /// let res = App::new("unlessone")
        ///     .arg(Arg::with_name("cfg")
        ///         .required_unless_one(&["dbg", "infile"])
        ///         .takes_value(true)
        ///         .long("config"))
        ///     .arg(Arg::with_name("dbg")
        ///         .long("debug"))
        ///     .arg(Arg::with_name("infile")
        ///         .short("i")
        ///         .takes_value(true))
        ///     .get_matches_from_safe(vec![
        ///         "unlessone"
        ///     ]);
        ///
        /// assert!(res.is_err());
        /// assert_eq!(res.unwrap_err().kind, ErrorKind::MissingRequiredArgument);
        /// ```
        pub fn required_unless_one(mut self, names: &[&'a str]) -> Self {
            if let Some(ref mut vec) = self.r_unless {
                for s in names {
                    vec.push(s);
                }
            } else {
                self.r_unless = Some(names.iter().map(|s| *s).collect::<Vec<_>>());
            }
            self.required(true)
        }

        /// Sets a conflicting argument by name. I.e. when using this argument,
        /// the following argument can't be present and vice versa.
        ///
        /// **NOTE:** Conflicting rules take precedence over being required by default. Conflict rules
        /// only need to be set for one of the two arguments, they do not need to be set for each.
        ///
        /// **NOTE:** Defining a conflict is two-way, but does *not* need to defined for both arguments
        /// (i.e. if A conflicts with B, defining A.conflicts_with(B) is sufficient. You do not need
        /// need to also do B.conflicts_with(A))
        ///
        /// # Examples
        ///
        /// ```rust
        /// # use clap::Arg;
        /// Arg::with_name("config")
        ///     .conflicts_with("debug")
        /// # ;
        /// ```
        ///
        /// Setting conflicting argument, and having both arguments present at runtime is an error.
        ///
        /// ```rust
        /// # use clap::{App, Arg, ErrorKind};
        /// let res = App::new("conflictions")
        ///     .arg(Arg::with_name("cfg")
        ///         .takes_value(true)
        ///         .conflicts_with("debug")
        ///         .long("config"))
        ///     .arg(Arg::with_name("debug")
        ///         .long("debug"))
        ///     .get_matches_from_safe(vec![
        ///         "conflictions", "--debug", "--config", "file.conf"
        ///     ]);
        ///
        /// assert!(res.is_err());
        /// assert_eq!(res.unwrap_err().kind, ErrorKind::ArgumentConflict);
        /// ```
        pub fn conflicts_with(mut self, name: &'a str) -> Self {
            if let Some(ref mut vec) = self.blacklist {
                vec.push(name);
            } else {
                self.blacklist = Some(vec![name]);
            }
            self
        }

        /// The same as `Arg::conflicts_with` but allows specifying multiple two-way conlicts per
        /// argument.
        ///
        /// **NOTE:** Conflicting rules take precedence over being required by default. Conflict rules
        /// only need to be set for one of the two arguments, they do not need to be set for each.
        ///
        /// **NOTE:** Defining a conflict is two-way, but does *not* need to defined for both arguments
        /// (i.e. if A conflicts with B, defining A.conflicts_with(B) is sufficient. You do not need
        /// need to also do B.conflicts_with(A))
        ///
        /// # Examples
        ///
        /// ```rust
        /// # use clap::Arg;
        /// Arg::with_name("config")
        ///     .conflicts_with_all(&["debug", "input"])
        /// # ;
        /// ```
        ///
        /// Setting conflicting argument, and having any of the arguments present at runtime with a
        /// conflicting argument is an error.
        ///
        /// ```rust
        /// # use clap::{App, Arg, ErrorKind};
        /// let res = App::new("conflictions")
        ///     .arg(Arg::with_name("cfg")
        ///         .takes_value(true)
        ///         .conflicts_with_all(&["debug", "input"])
        ///         .long("config"))
        ///     .arg(Arg::with_name("debug")
        ///         .long("debug"))
        ///     .arg(Arg::with_name("input")
        ///         .index(1))
        ///     .get_matches_from_safe(vec![
        ///         "conflictions", "--config", "file.conf", "file.txt"
        ///     ]);
        ///
        /// assert!(res.is_err());
        /// assert_eq!(res.unwrap_err().kind, ErrorKind::ArgumentConflict);
        /// ```
        pub fn conflicts_with_all(mut self, names: &[&'a str]) -> Self {
            if let Some(ref mut vec) = self.blacklist {
                for s in names {
                    vec.push(s);
                }
            } else {
                self.blacklist = Some(names.iter().map(|s| *s).collect::<Vec<_>>());
            }
            self
        }

        /// Sets a overridable argument by name. I.e. this argument and the following argument
        /// will override each other in POSIX style (whichever argument was specified at runtime
        /// **last** "wins")
        ///
        /// **NOTE:** When an argument is overriden it is essentially as if it never was used, any
        /// conflicts, requirements, etc. are evaluated **after** all "overrides" have been removed
        ///
        /// # Examples
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// let m = App::new("posix")
        ///     .arg(Arg::from_usage("-f, --flag 'some flag'")
        ///         .conflicts_with("debug"))
        ///     .arg(Arg::from_usage("-d, --debug 'other flag'"))
        ///     .arg(Arg::from_usage("-c, --color 'third flag'")
        ///         .overrides_with("flag"))
        ///     .get_matches_from(vec!["posix", "-f", "-d", "-c"]);
        ///                                 //    ^~~~~~~~~~~~^~~~~ flag is overriden by color
        ///
        /// assert!(m.is_present("color"));
        /// assert!(m.is_present("debug")); // even though flag conflicts with debug, it's as if flag
        ///                                 // was never used because it was overriden with color
        /// assert!(!m.is_present("flag"));
        /// ```
        pub fn overrides_with(mut self, name: &'a str) -> Self {
            if let Some(ref mut vec) = self.overrides {
                vec.push(name.as_ref());
            } else {
                self.overrides = Some(vec![name.as_ref()]);
            }
            self
        }

        /// Sets multiple mutually overridable arguments by name. I.e. this argument and the following
        /// argument will override each other in POSIX style (whichever argument was specified at
        /// runtime **last** "wins")
        ///
        /// **NOTE:** When an argument is overriden it is essentially as if it never was used, any
        /// conflicts, requirements, etc. are evaluated **after** all "overrides" have been removed
        ///
        /// # Examples
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// let m = App::new("posix")
        ///     .arg(Arg::from_usage("-f, --flag 'some flag'")
        ///         .conflicts_with("color"))
        ///     .arg(Arg::from_usage("-d, --debug 'other flag'"))
        ///     .arg(Arg::from_usage("-c, --color 'third flag'")
        ///         .overrides_with_all(&["flag", "debug"]))
        ///     .get_matches_from(vec!["posix", "-f", "-d", "-c"]);
        ///                                 //    ^~~~~~^~~~~~~~~ flag and debug are overriden by color
        ///
        /// assert!(m.is_present("color")); // even though flag conflicts with color, it's as if flag
        ///                                 // and debug were never used because they were overriden
        ///                                 // with color
        /// assert!(!m.is_present("debug"));
        /// assert!(!m.is_present("flag"));
        /// ```
        pub fn overrides_with_all(mut self, names: &[&'a str]) -> Self {
            if let Some(ref mut vec) = self.overrides {
                for s in names {
                    vec.push(s);
                }
            } else {
                self.overrides = Some(names.iter().map(|s| *s).collect::<Vec<_>>());
            }
            self
        }

        /// Sets an argument by name that is required when this one is present I.e. when
        /// using this argument, the following argument *must* be present.
        ///
        /// **NOTE:** Conflicting rules and override rules take precedence over being required
        ///
        /// # Examples
        ///
        /// ```rust
        /// # use clap::Arg;
        /// Arg::with_name("config")
        ///     .requires("input")
        /// # ;
        /// ```
        ///
        /// Setting `requires("arg")` requires that the argument be used at runtime if the defining
        /// argument is used. If the defining argument isn't used, the other arguemnt isn't required
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// let res = App::new("reqtest")
        ///     .arg(Arg::with_name("cfg")
        ///         .takes_value(true)
        ///         .requires("input")
        ///         .long("config"))
        ///     .arg(Arg::with_name("input")
        ///         .index(1))
        ///     .get_matches_from_safe(vec![
        ///         "reqtest"
        ///     ]);
        ///
        /// assert!(res.is_ok()); // We didn't use cfg, so input wasn't required
        /// ```
        ///
        /// Setting `requires("arg")` and *not* supplying that argument is an error.
        ///
        /// ```rust
        /// # use clap::{App, Arg, ErrorKind};
        /// let res = App::new("reqtest")
        ///     .arg(Arg::with_name("cfg")
        ///         .takes_value(true)
        ///         .requires("input")
        ///         .long("config"))
        ///     .arg(Arg::with_name("input")
        ///         .index(1))
        ///     .get_matches_from_safe(vec![
        ///         "reqtest", "--config", "file.conf"
        ///     ]);
        ///
        /// assert!(res.is_err());
        /// assert_eq!(res.unwrap_err().kind, ErrorKind::MissingRequiredArgument);
        /// ```
        pub fn requires(mut self, name: &'a str) -> Self {
            if let Some(ref mut vec) = self.requires {
                vec.push(name);
            } else {
                self.requires = Some(vec![name]);
            }
            self
        }

        /// Sets multiple arguments by names that are required when this one is present I.e. when
        /// using this argument, the following arguments *must* be present.
        ///
        /// **NOTE:** Mutually exclusive and override rules take precedence over being required
        /// by default.
        ///
        /// # Examples
        ///
        /// ```rust
        /// # use clap::Arg;
        /// Arg::with_name("config")
        ///     .requires_all(&["input", "output"])
        /// # ;
        /// ```
        ///
        /// Setting `requires_all(&["arg", "arg2"])` requires that all the arguments be used at runtime
        /// if the defining argument is used. If the defining argument isn't used, the other arguemnt
        /// isn't required
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// let res = App::new("reqtest")
        ///     .arg(Arg::with_name("cfg")
        ///         .takes_value(true)
        ///         .requires("input")
        ///         .long("config"))
        ///     .arg(Arg::with_name("input")
        ///         .index(1))
        ///     .arg(Arg::with_name("output")
        ///         .index(2))
        ///     .get_matches_from_safe(vec![
        ///         "reqtest"
        ///     ]);
        ///
        /// assert!(res.is_ok()); // We didn't use cfg, so input and output weren't required
        /// ```
        ///
        /// Setting `requires_all(&["arg", "arg2"])` and *not* supplying all the arguments is an error.
        ///
        /// ```rust
        /// # use clap::{App, Arg, ErrorKind};
        /// let res = App::new("reqtest")
        ///     .arg(Arg::with_name("cfg")
        ///         .takes_value(true)
        ///         .requires_all(&["input", "output"])
        ///         .long("config"))
        ///     .arg(Arg::with_name("input")
        ///         .index(1))
        ///     .arg(Arg::with_name("output")
        ///         .index(2))
        ///     .get_matches_from_safe(vec![
        ///         "reqtest", "--config", "file.conf", "in.txt"
        ///     ]);
        ///
        /// assert!(res.is_err());
        /// // We didn't use output
        /// assert_eq!(res.unwrap_err().kind, ErrorKind::MissingRequiredArgument);
        /// ```
        pub fn requires_all(mut self, names: &[&'a str]) -> Self {
            if let Some(ref mut vec) = self.requires {
                for s in names {
                    vec.push(s);
                }
            } else {
                self.requires = Some(names.into_iter().map(|s| *s).collect::<Vec<_>>());
            }
            self
        }

        /// Specifies that the argument takes a value at run time.
        ///
        /// **NOTE:** values for arguments may be specified in any of the following methods
        ///
        /// * Using a space such as `-o value` or `--option value`
        /// * Using an equals and no space such as `-o=value` or `--option=value`
        /// * Use a short and no space such as `-ovalue`
        ///
        /// **NOTE:** By default, values are delimted by commas, meaning `--option=val1,val2,val3` is
        /// is three values for the `--option` argument. If you wish to change the delimiter to another
        /// character you can use `Arg::value_delimiter(char)`, alternatively you can delimiting values
        /// **OFF** by using `Arg::use_delimiter(false)`
        ///
        /// # Examples
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// Arg::with_name("config")
        ///     .takes_value(true)
        /// # ;
        /// ```
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// let m = App::new("posvals")
        ///     .arg(Arg::with_name("mode")
        ///         .long("mode")
        ///         .takes_value(true))
        ///     .get_matches_from(vec!["posvals", "--mode", "fast"]);
        ///
        /// assert!(m.is_present("mode"));
        /// assert_eq!(m.value_of("mode"), Some("fast"));
        /// ```
        pub fn takes_value(self, tv: bool) -> Self {
            if tv { self.set(ArgSettings::TakesValue) } else { self.unset(ArgSettings::TakesValue) }
        }

        /// Specifies the index of a positional argument **starting at** 1.
        ///
        /// **NOTE:** The index refers to position according to **other positional argument**. It does
        /// not define position in the argument list as a whole.
        ///
        /// **NOTE:** If no `short`, or `long` have been defined, you can optionally leave off the
        /// `index` method, and the index will be assigned in order of evaluation. Utilizing the
        /// `index` method allows for setting indexes out of order
        ///
        /// **NOTE:** When utilized with `multiple(true)`, only the **last** psoitional argument may
        /// be defined as multiple (i.e. with the highest index)
        ///
        /// # Panics
        ///
        /// Although not in this method directly, `App` will `panic!` if indexes are skipped (such as
        /// defining `index(1)` and `index(3)` but not `index(2)`, or a positional argument is defined
        /// as multiple and is not the highest index
        ///
        /// # Examples
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// Arg::with_name("config")
        ///     .index(1)
        /// # ;
        /// ```
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// let m = App::new("posvals")
        ///     .arg(Arg::with_name("mode")
        ///         .index(1))
        ///     .arg(Arg::with_name("debug")
        ///         .long("debug"))
        ///     .get_matches_from(vec!["posvals", "--debug", "fast"]);
        ///
        /// assert!(m.is_present("mode"));
        /// assert_eq!(m.value_of("mode"), Some("fast")); // notice index(1) means "first positional"
        ///                                               // *not* first argument
        /// ```
        pub fn index(mut self, idx: u64) -> Self {
            self.index = Some(idx);
            self
        }

        /// Specifies that the argument may appear more than once. For flags, this results
        /// in the number of occurrences of the flag being recorded. For example `-ddd` or `-d -d -d`
        /// would count as three occurrences. For options there is a distinct difference in multiple
        /// occurrences vs multiple values.
        ///
        /// For example, `--opt val1 val2` is one occurrence, but two values. Whereas
        /// `--opt val1 --opt val2` is two occurrences.
        ///
        /// **WARNING:**
        ///
        /// Setting `multipe(true)` for an option allows multiple values **and** multiple occurrences
        /// because it isn't possible to more occurrences than values for options. Because multiple
        /// values are allowed, `--option val1 val2 val3` is perfectly valid, be careful when designing
        /// a CLI where positional arguments are expectd after a option which accepts multiple values,
        /// as `clap` will continue parsing *values* until it reaches the max or specific number of values defined, or another flag
        /// or option.
        ///
        /// **Pro Tip**:
        ///
        /// It's possible to define an option which allows multiple occurrences, but only one value per
        /// occurrence. To do this use `Arg::number_of_values(1)` in coordination with
        /// `Arg::multiple(true)`.
        ///
        /// # Examples
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// Arg::with_name("debug")
        ///     .short("d")
        ///     .multiple(true)
        /// # ;
        /// ```
        /// An example with flags
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// let m = App::new("mults")
        ///     .arg(Arg::with_name("verbose")
        ///         .multiple(true)
        ///         .short("v"))
        ///     .get_matches_from(vec!["mults", "-v", "-v", "-v"]); // note, -vvv would have same result
        ///
        /// assert!(m.is_present("verbose"));
        /// assert_eq!(m.occurrences_of("verbose"), 3);
        /// ```
        ///
        /// An example with options
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// let m = App::new("mults")
        ///     .arg(Arg::with_name("file")
        ///         .multiple(true)
        ///         .takes_value(true)
        ///         .short("F"))
        ///     .get_matches_from(vec!["mults", "-F", "file1", "file2", "file3"]);
        ///
        /// assert!(m.is_present("file"));
        /// assert_eq!(m.occurrences_of("file"), 1); // notice only one occurrence
        /// let files: Vec<_> = m.values_of("file").unwrap().collect();
        /// assert_eq!(files, ["file1", "file2", "file3"]);
        /// ```
        /// This is functionally equivilant to the example above
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// let m = App::new("mults")
        ///     .arg(Arg::with_name("file")
        ///         .multiple(true)
        ///         .takes_value(true)
        ///         .short("F"))
        ///     .get_matches_from(vec!["mults", "-F", "file1", "-F", "file2", "-F", "file3"]);
        /// let files: Vec<_> = m.values_of("file").unwrap().collect();
        /// assert_eq!(files, ["file1", "file2", "file3"]);
        ///
        /// assert!(m.is_present("file"));
        /// assert_eq!(m.occurrences_of("file"), 3); // Notice 3 occurrences
        /// let files: Vec<_> = m.values_of("file").unwrap().collect();
        /// assert_eq!(files, ["file1", "file2", "file3"]);
        /// ```
        ///
        /// A common mistake is to define an option which allows multiples, and a positional argument
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// let m = App::new("mults")
        ///     .arg(Arg::with_name("file")
        ///         .multiple(true)
        ///         .takes_value(true)
        ///         .short("F"))
        ///     .arg(Arg::with_name("word")
        ///         .index(1))
        ///     .get_matches_from(vec!["mults", "-F", "file1", "file2", "file3", "word"]);
        ///
        /// assert!(m.is_present("file"));
        /// let files: Vec<_> = m.values_of("file").unwrap().collect();
        /// assert_eq!(files, ["file1", "file2", "file3", "word"]); // wait...what?!
        /// assert!(!m.is_present("word")); // but we clearly used word!
        /// ```
        /// The problem is clap doesn't know when to stop parsing values for "files". This is further
        /// compounded by if we'd said `word -F file1 file2` it would have worked fine, so it would
        /// appear to only fail sometimes...not good!
        ///
        /// A solution for the example above is to specify that `-F` only accepts one value, but is
        /// allowed to appear multiple times
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// let m = App::new("mults")
        ///     .arg(Arg::with_name("file")
        ///         .multiple(true)
        ///         .takes_value(true)
        ///         .number_of_values(1)
        ///         .short("F"))
        ///     .arg(Arg::with_name("word")
        ///         .index(1))
        ///     .get_matches_from(vec!["mults", "-F", "file1", "-F", "file2", "-F", "file3", "word"]);
        ///
        /// assert!(m.is_present("file"));
        /// let files: Vec<_> = m.values_of("file").unwrap().collect();
        /// assert_eq!(files, ["file1", "file2", "file3"]);
        /// assert!(m.is_present("word"));
        /// assert_eq!(m.value_of("word"), Some("word"));
        /// ```
        /// As a final example, notice if we define `number_of_values(1)` and try to run the problem
        /// example above, it would have been a runtime error with a pretty message to the user :)
        ///
        /// ```rust
        /// # use clap::{App, Arg, ErrorKind};
        /// let res = App::new("mults")
        ///     .arg(Arg::with_name("file")
        ///         .multiple(true)
        ///         .takes_value(true)
        ///         .number_of_values(1)
        ///         .short("F"))
        ///     .arg(Arg::with_name("word")
        ///         .index(1))
        ///     .get_matches_from_safe(vec!["mults", "-F", "file1", "file2", "file3", "word"]);
        ///
        /// assert!(res.is_err());
        /// assert_eq!(res.unwrap_err().kind, ErrorKind::UnknownArgument);
        /// ```
        pub fn multiple(self, multi: bool) -> Self {
            if multi { self.set(ArgSettings::Multiple) } else { self.unset(ArgSettings::Multiple) }
        }

        /// Specifies that an argument can be matched to all child subcommands.
        ///
        /// **NOTE:** Global arguments *only* propagate down, **not** up (to parent commands)
        ///
        /// **NOTE:** Global arguments *cannot* be required.
        ///
        /// **NOTE:** Global arguments, when matched, *only* exist in the command's matches that they
        /// were matched to. For example, if you defined a `--flag` global argument in the top most
        /// parent command, but the user supplied the arguments `top cmd1 cmd2 --flag` *only* `cmd2`'s
        /// `ArgMatches` would return `true` if tested for `.is_present("flag")`.
        ///
        /// # Examples
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// Arg::with_name("debug")
        ///     .short("d")
        ///     .global(true)
        /// # ;
        /// ```
        ///
        /// For example, assume an appliction with two subcommands, and you'd like to define a
        /// `--verbose` flag that can be called on any of the subcommands and parent, but you don't
        /// want to clutter the source with three duplicate `Arg` definitions.
        ///
        /// ```rust
        /// # use clap::{App, Arg, SubCommand};
        /// let m = App::new("mults")
        ///     .arg(Arg::with_name("verb")
        ///         .long("verbose")
        ///         .short("v")
        ///         .global(true))
        ///     .subcommand(SubCommand::with_name("test"))
        ///     .subcommand(SubCommand::with_name("do-stuff"))
        ///     .get_matches_from(vec!["mults", "do-stuff", "--verbose"]);
        ///
        /// assert_eq!(m.subcommand_name(), Some("do-stuff"));
        /// let sub_m = m.subcommand_matches("do-stuff").unwrap();
        /// assert!(sub_m.is_present("verb"));
        /// ```
        pub fn global(self, g: bool) -> Self {
            if g { self.set(ArgSettings::Global) } else { self.unset(ArgSettings::Global) }
        }

        /// Allows an argument to accept explicitly empty values. An empty value must be specified at
        /// the command line with an explicit `""`, or `''`
        ///
        /// **NOTE:** Defaults to `true` (Explicitly empty values are allowed)
        ///
        /// **NOTE:** Implicitly sets `takes_value(true)` when set to `false`
        ///
        /// # Examples
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// Arg::with_name("file")
        ///     .long("file")
        ///     .empty_values(false)
        /// # ;
        /// ```
        /// The default is to allow empty values, such as `--option ""` would be an empty value. But
        /// we can change to make empty values become an error.
        ///
        /// ```rust
        /// # use clap::{App, Arg, ErrorKind};
        /// let res = App::new("evals")
        ///     .arg(Arg::with_name("cfg")
        ///         .long("config")
        ///         .short("v")
        ///         .empty_values(false))
        ///     .get_matches_from_safe(vec!["evals", "--config="]);
        ///
        /// assert!(res.is_err());
        /// assert_eq!(res.unwrap_err().kind, ErrorKind::EmptyValue);
        /// ```
        pub fn empty_values(mut self, ev: bool) -> Self {
            if ev {
                self.set(ArgSettings::EmptyValues)
            } else {
                self = self.set(ArgSettings::TakesValue);
                self.unset(ArgSettings::EmptyValues)
            }
        }

        /// Hides an argument from help message output.
        ///
        /// **NOTE:** This does **not** hide the argument from usage strings on error
        ///
        /// # Examples
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// Arg::with_name("debug")
        ///     .hidden(true)
        /// # ;
        /// ```
        /// Setting `hidden(true)` will hide the argument when displaying help text
        ///
        /// ```ignore
        /// # use clap::{App, Arg};
        /// let m = App::new("helptest")
        ///     .arg(Arg::with_name("cfg")
        ///         .long("config")
        ///         .hidden(true)
        ///         .help("Some help text describing the --config arg"))
        ///     .get_matches_from(vec![
        ///         "shorttest", "--help"
        ///     ]);
        ///
        /// // ...
        /// ```
        ///
        /// The above example displays
        ///
        /// ```notrust
        /// helptest
        ///
        /// USAGE:
    	///    helptest [FLAGS]
        ///
        /// FLAGS:
        /// -h, --help       Prints help information
        /// -V, --version    Prints version information
        /// ```
        pub fn hidden(self, h: bool) -> Self {
            if h { self.set(ArgSettings::Hidden) } else { self.unset(ArgSettings::Hidden) }
        }

        /// Specifies a list of possible values for this argument. At runtime, `clap` verifies that only
        /// one of the specified values was used, or fails with an error message.
        ///
        /// **NOTE:** This setting only applies to options and positional arguments
        ///
        /// # Examples
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// Arg::with_name("mode")
        ///     .takes_value(true)
        ///     .possible_values(&["fast", "slow", "medium"])
        /// # ;
        /// ```
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// let m = App::new("posvals")
        ///     .arg(Arg::with_name("mode")
        ///         .long("mode")
        ///         .takes_value(true)
        ///         .possible_values(&["fast", "slow", "medium"]))
        ///     .get_matches_from(vec!["posvals", "--mode", "fast"]);
        /// assert!(m.is_present("mode"));
        /// assert_eq!(m.value_of("mode"), Some("fast"));
        /// ```
        ///
        /// The next example shows a failed parse from using a value which wasn't defined as one of the
        /// possible values.
        ///
        /// ```rust
        /// # use clap::{App, Arg, ErrorKind};
        /// let res = App::new("posvals")
        ///     .arg(Arg::with_name("mode")
        ///         .long("mode")
        ///         .takes_value(true)
        ///         .possible_values(&["fast", "slow", "medium"]))
        ///     .get_matches_from_safe(vec!["myprog", "--mode", "wrong"]);
        /// assert!(res.is_err());
        /// assert_eq!(res.unwrap_err().kind, ErrorKind::InvalidValue);
        /// ```
        pub fn possible_values(mut self, names: &[&'b str]) -> Self {
            if let Some(ref mut vec) = self.possible_vals {
                for s in names {
                    vec.push(s);
                }
            } else {
                self.possible_vals = Some(names.iter().map(|s| *s).collect::<Vec<_>>());
            }
            self
        }

        /// Specifies a possible value for this argument, one at a time. At runtime, `clap` verifies
        /// that only one of the specified values was used, or fails with error message.
        ///
        /// # Examples
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// Arg::with_name("mode")
        ///     .takes_value(true)
        ///     .possible_value("fast")
        ///     .possible_value("slow")
        ///     .possible_value("medium")
        /// # ;
        /// ```
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// let m = App::new("posvals")
        ///     .arg(Arg::with_name("mode")
        ///         .long("mode")
        ///         .takes_value(true)
        ///         .possible_value("fast")
        ///         .possible_value("slow")
        ///         .possible_value("medium"))
        ///     .get_matches_from(vec!["posvals", "--mode", "fast"]);
        /// assert!(m.is_present("mode"));
        /// assert_eq!(m.value_of("mode"), Some("fast"));
        /// ```
        ///
        /// The next example shows a failed parse from using a value which wasn't defined as one of the
        /// possible values.
        ///
        /// ```rust
        /// # use clap::{App, Arg, ErrorKind};
        /// let res = App::new("posvals")
        ///     .arg(Arg::with_name("mode")
        ///         .long("mode")
        ///         .takes_value(true)
        ///         .possible_value("fast")
        ///         .possible_value("slow")
        ///         .possible_value("medium"))
        ///     .get_matches_from_safe(vec!["myprog", "--mode", "wrong"]);
        /// assert!(res.is_err());
        /// assert_eq!(res.unwrap_err().kind, ErrorKind::InvalidValue);
        /// ```
        pub fn possible_value(mut self, name: &'b str) -> Self {
            if let Some(ref mut vec) = self.possible_vals {
                vec.push(name);
            } else {
                self.possible_vals = Some(vec![name]);
            }
            self
        }

        /// Specifies the name of the group the argument belongs to.
        ///
        /// # Examples
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// Arg::with_name("debug")
        ///     .long("debug")
        ///     .group("mode")
        /// # ;
        /// ```
        ///
        /// Multiple arguments can be a member of a single group and then the group checked as if it
        /// was one of said arguments.
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// let m = App::new("groups")
        ///     .arg(Arg::with_name("debug")
        ///         .long("debug")
        ///         .group("mode"))
        ///     .arg(Arg::with_name("verbose")
        ///         .long("verbose")
        ///         .group("mode"))
        ///     .get_matches_from(vec!["posvals", "--debug"]);
        /// assert!(m.is_present("mode"));
        /// ```
        pub fn group(mut self, name: &'a str) -> Self {
            self.group = Some(name);
            self
        }

        /// Specifies how many values are required to satisfy this argument. For example, if you had a
        /// `-f <file>` argument where you wanted exactly 3 'files' you would set
        /// `.number_of_values(3)`, and this argument wouldn't be satisfied unless the user provided
        /// 3 and only 3 values.
        ///
        /// **NOTE:** Does *not* require `.multiple(true)` to be set. Setting `.multiple(true)` would
        /// allow `-f <file> <file> <file> -f <file> <file> <file>` where as *not* setting
        /// `.multiple(true)` would only allow one occurrence of this argument.
        ///
        /// # Examples
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// Arg::with_name("file")
        ///     .short("f")
        ///     .number_of_values(3)
        /// # ;
        /// ```
        ///
        /// Not supplying the correct number of values is an error
        ///
        /// ```rust
        /// # use clap::{App, Arg, ErrorKind};
        /// let res = App::new("numvals")
        ///     .arg(Arg::with_name("file")
        ///         .takes_value(true)
        ///         .number_of_values(2)
        ///         .short("F"))
        ///     .get_matches_from_safe(vec!["mults", "-F", "file1"]);
        ///
        /// assert!(res.is_err());
        /// assert_eq!(res.unwrap_err().kind, ErrorKind::WrongNumberOfValues);
        /// ```
        pub fn number_of_values(mut self, qty: u64) -> Self {
            self.num_vals = Some(qty);
            self
        }

        /// Allows one to perform a custom validation on the argument value. You provide a closure which
        /// accepts a `String` value, a `Result` where the `Err(String)` is a message displayed to the
        /// user.
        ///
        /// **NOTE:** The error message does *not* need to contain the `error:` portion, only the
        /// message.
        ///
        /// **NOTE:** There is a small performance hit for using validators, as they are implemented
        /// with `Rc` pointers. And the value to be checked will be allocated an extra time in order to
        /// to be passed to the closure. This performance hit is extremely minimal in the grand scheme
        /// of things.
        ///
        /// # Examples
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// fn has_at(v: String) -> Result<(), String> {
        ///     if v.contains("@") { return Ok(()); }
        ///     Err(String::from("The value did not contain the required @ sigil"))
        /// }
        /// let res = App::new("validators")
        ///     .arg(Arg::with_name("file")
        ///         .index(1)
        ///         .validator(has_at))
        ///     .get_matches_from_safe(vec![
        ///         "validators", "some@file"
        ///     ]);
        /// assert!(res.is_ok());
        /// assert_eq!(res.unwrap().value_of("file"), Some("some@file"));
        /// ```
        pub fn validator<F>(mut self, f: F) -> Self
            where F: Fn(String) -> Result<(), String> + 'static
        {
            self.validator = Some(Rc::new(f));
            self
        }

        /// Specifies the *maximum* number of values are for this argument. For example, if you had a
        /// `-f <file>` argument where you wanted up to 3 'files' you would set
        /// `.max_values(3)`, and this argument would be satisfied if the user provided, 1, 2, or 3
        /// values.
        ///
        /// **NOTE:** This does not implicitly set `mulitple(true)`. This is because `-o val -o val` is
        /// multiples occurrences but a single value and `-o val1 val2` is a single occurence with
        /// multple values. For positional arguments this **does** set `multiple(true)` because there
        /// is no way to determine the diffrence between multiple occureces and multiple values.
        ///
        /// # Examples
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// Arg::with_name("file")
        ///     .short("f")
        ///     .max_values(3)
        /// # ;
        /// ```
        ///
        /// Supplying less than the maximum number of values is allowed
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// let res = App::new("numvals")
        ///     .arg(Arg::with_name("file")
        ///         .takes_value(true)
        ///         .max_values(3)
        ///         .short("F"))
        ///     .get_matches_from_safe(vec!["mults", "-F", "file1", "file2"]);
        ///
        /// assert!(res.is_ok());
        /// let m = res.unwrap();
        /// let files: Vec<_> = m.values_of("file").unwrap().collect();
        /// assert_eq!(files, ["file1", "file2"]);
        /// ```
        ///
        /// Supplying more than the maximum number of values is an error
        ///
        /// ```rust
        /// # use clap::{App, Arg, ErrorKind};
        /// let res = App::new("numvals")
        ///     .arg(Arg::with_name("file")
        ///         .takes_value(true)
        ///         .max_values(2)
        ///         .short("F"))
        ///     .get_matches_from_safe(vec!["mults", "-F", "file1", "file2", "file3"]);
        ///
        /// assert!(res.is_err());
        /// assert_eq!(res.unwrap_err().kind, ErrorKind::TooManyValues);
        /// ```
        pub fn max_values(mut self, qty: u64) -> Self {
            self.max_vals = Some(qty);
            self
        }

        /// Specifies the *minimum* number of values are for this argument. For example, if you had a
        /// `-f <file>` argument where you wanted at least 2 'files' you would set
        /// `.min_values(2)`, and this argument would be satisfied if the user provided, 2 or more
        /// values.
        ///
        /// **NOTE:** This does not implicitly set `mulitple(true)`. This is because `-o val -o val` is
        /// multiples occurrences but a single value and `-o val1 val2` is a single occurence with
        /// multple values. For positional arguments this **does** set `multiple(true)` because there
        /// is no way to determine the diffrence between multiple occureces and multiple values.
        ///
        /// # Examples
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// Arg::with_name("file")
        ///     .short("f")
        ///     .min_values(3)
        /// # ;
        /// ```
        ///
        /// Supplying more than the minimum number of values is allowed
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// let res = App::new("numvals")
        ///     .arg(Arg::with_name("file")
        ///         .takes_value(true)
        ///         .min_values(2)
        ///         .short("F"))
        ///     .get_matches_from_safe(vec!["mults", "-F", "file1", "file2", "file3"]);
        ///
        /// assert!(res.is_ok());
        /// let m = res.unwrap();
        /// let files: Vec<_> = m.values_of("file").unwrap().collect();
        /// assert_eq!(files, ["file1", "file2", "file3"]);
        /// ```
        ///
        /// Supplying less than the mainimum number of values is an error
        ///
        /// ```rust
        /// # use clap::{App, Arg, ErrorKind};
        /// let res = App::new("numvals")
        ///     .arg(Arg::with_name("file")
        ///         .takes_value(true)
        ///         .min_values(2)
        ///         .short("F"))
        ///     .get_matches_from_safe(vec!["mults", "-F", "file1"]);
        ///
        /// assert!(res.is_err());
        /// assert_eq!(res.unwrap_err().kind, ErrorKind::TooFewValues);
        /// ```
        pub fn min_values(mut self, qty: u64) -> Self {
            self.min_vals = Some(qty);
            self.set(ArgSettings::TakesValue)
        }

        /// Specifies whether or not an arugment should allow grouping of multiple values via a
        /// delimter. I.e. shoulde `--option=val1,val2,val3` be parsed as three values (`val1`, `val2`,
        /// and `val3`) or as a single value (`val1,val2,val3`). Defaults to using `,` (comma) as the
        /// value delimiter for all arguments that accept values (options and positional arguments)
        ///
        /// **NOTE:** The defalt is `true`. Setting the value to `true` will reset any previous use of
        /// `Arg::value_delimiter` back to the default of `,` (comma).
        ///
        /// # Examples
        ///
        /// The following example shows the default behavior.
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// let delims = App::new("delims")
        ///     .arg(Arg::with_name("option")
        ///         .long("option")
        ///         .takes_value(true))
        ///     .get_matches_from(vec![
        ///         "delims",
        ///         "--option=val1,val2,val3",
        ///     ]);
        ///
        /// assert!(delims.is_present("option"));
        /// assert_eq!(delims.occurrences_of("option"), 1);
        /// assert_eq!(delims.values_of("option").unwrap().collect::<Vec<_>>(), ["val1", "val2", "val3"]);
        /// ```
        /// The next example shows the difference when turning delimiters off.
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// let nodelims = App::new("nodelims")
        ///     .arg(Arg::with_name("option")
        ///         .long("option")
        ///         .use_delimiter(false)
        ///         .takes_value(true))
        ///     .get_matches_from(vec![
        ///         "nodelims",
        ///         "--option=val1,val2,val3",
        ///     ]);
        ///
        /// assert!(nodelims.is_present("option"));
        /// assert_eq!(nodelims.occurrences_of("option"), 1);
        /// assert_eq!(nodelims.value_of("option").unwrap(), "val1,val2,val3");
        /// ```
        pub fn use_delimiter(mut self, d: bool) -> Self {
            if d {
                self.val_delim = Some(',');
                self.set(ArgSettings::UseValueDelimiter)
            } else {
                self.val_delim = None;
                self.unset(ArgSettings::UseValueDelimiter)
            }
        }

        /// Specifies the separator to use when values are clumped together, defaults to `,` (comma).
        ///
        /// **NOTE:** implicitly sets `Arg::use_delimiter(true)`
        ///
        /// **NOTE:** implicitly sets `Arg::takes_value(true)`
        ///
        /// # Examples
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// let app = App::new("fake")
        ///     .arg(Arg::with_name("config")
        ///         .short("c")
        ///         .long("config")
        ///         .value_delimiter(";"));
        ///
        /// let m = app.get_matches_from(vec![
        ///     "fake", "--config=val1;val2;val3"
        /// ]);
        ///
        /// assert_eq!(m.values_of("config").unwrap().collect::<Vec<_>>(), ["val1", "val2", "val3"])
        /// ```
        pub fn value_delimiter(mut self, d: &str) -> Self {
            self = self.set(ArgSettings::TakesValue);
            self = self.set(ArgSettings::UseValueDelimiter);
            self.val_delim = Some(d.chars()
                                   .nth(0)
                                   .expect("Failed to get value_delimiter from arg"));
            self
        }

        /// Specify multiple names for values of option arguments. These names are cosmetic only, used
        /// for help and usage strings only. The names are **not** used to access arguments. The values
        /// of the arguments are accessed in numeric order (i.e. if you specify two names `one` and
        /// `two` `one` will be the first matched value, `two` will be the second).
        ///
        /// This setting can be very helpful when describing the type of input the user should be
        /// using, such as `FILE`, `INTERFACE`, etc. Although not required, it's somewhat convention to
        /// use all capital letters for the value name.
        ///
        /// **Pro Tip:** It may help to use `Arg::next_line_help(true)` if there are long, or multiple
        /// value names in order to not throw off the help text alignment of all options.
        ///
        /// **NOTE:** This implicitly sets `.number_of_values()` if the number of value names is
        /// greater than one. I.e. be aware that the number of "names" you set for the values, will be
        /// the *exact* number of values required to satisfy this argument
        ///
        /// **NOTE:** implicitly sets `Arg::takes_value(true)`
        ///
        /// **NOTE:** Does *not* require or imply `.multiple(true)`.
        ///
        /// # Examples
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// Arg::with_name("speed")
        ///     .short("s")
        ///     .value_names(&["fast", "slow"])
        /// # ;
        /// ```
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// let app = App::new("valnames")
        ///     .arg(Arg::with_name("io")
        ///         .long("io-files")
        ///         .value_names(&["INFILE", "OUTFILE"]))
        ///     .get_matches_from(vec![
        ///         "valnames", "--help"
        ///     ]);
        /// ```
        /// Running the above program produces the following output
        ///
        /// ```notrust
        /// valnames
        ///
        /// USAGE:
    	///    valnames [FLAGS] [OPTIONS]
        ///
        /// FLAGS:
        ///     -h, --help       Prints help information
        ///     -V, --version    Prints version information
        ///
        /// OPTIONS:
        ///     --io-files <INFILE> <OUTFILE>    Some help text
        /// ```
        pub fn value_names(mut self, names: &[&'b str]) -> Self {
            self.setb(ArgSettings::TakesValue);
            if let Some(ref mut vals) = self.val_names {
                let mut l =  vals.len();
                for s in names {
                    vals.insert(l, s);
                    l += 1;
                }
            } else {
                let mut vm = VecMap::new();
                for (i, n) in names.iter().enumerate() {
                    vm.insert(i, *n);
                }
                self.val_names = Some(vm);
            }
            self
        }

        /// Specifies the name for value of option or positional arguments inside of help documenation.
        /// This name is cosmetic only, the name is **not** used to access arguments. This setting can
        /// be very helpful when describing the type of input the user should be using, such as `FILE`,
        /// `INTERFACE`, etc. Although not required, it's somewhat convention to use all capital
        /// letters for the value name.
        ///
        /// **NOTE:** implicitly sets `Arg::takes_value(true)`
        ///
        /// # Examples
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// Arg::with_name("cfg")
        ///     .long("config")
        ///     .value_name("FILE")
        /// # ;
        /// ```
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// let app = App::new("valnames")
        ///     .arg(Arg::with_name("config")
        ///         .long("config")
        ///         .value_name("FILE"))
        ///     .get_matches_from(vec![
        ///         "valnames", "--help"
        ///     ]);
        /// ```
        /// Running the above program produces the following output
        ///
        /// ```notrust
        /// valnames
        ///
        /// USAGE:
    	///    valnames [FLAGS] [OPTIONS]
        ///
        /// FLAGS:
        ///     -h, --help       Prints help information
        ///     -V, --version    Prints version information
        ///
        /// OPTIONS:
        ///     --config <FILE>     Some help text
        /// ```
        pub fn value_name(mut self, name: &'b str) -> Self {
            self.setb(ArgSettings::TakesValue);
            if let Some(ref mut vals) = self.val_names {
                let l = vals.len();
                vals.insert(l, name);
            } else {
                let mut vm = VecMap::new();
                vm.insert(0, name);
                self.val_names = Some(vm);
            }
            self
        }

        /// Specifies the value of the argument when *not* specified at runtime.
        ///
        /// **NOTE:** If the user *does not* use this argument at runtime, `ArgMatches::occurrences_of`
        /// will return `0` even though the `value_of` will return the default specified.
        ///
        /// **NOTE:** If the user *does not* use this argument at runtime `ArgMatches::is_present` will
        /// still return `true`. If you wish to determine whether the argument was used at runtime or
        /// not, consider `ArgMatches::occurrences_of` which will return `0` if the argument was *not*
        /// used at runtmie.
        ///
        /// **NOTE:** This implicitly sets `Arg::takes_value(true)`.
        ///
        /// # Examples
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// let m = App::new("defvals")
        ///     .arg(Arg::with_name("opt")
        ///         .long("myopt")
        ///         .default_value("myval"))
        ///     .get_matches_from(vec![
        ///         "defvals"
        ///     ]);
        ///
        /// assert_eq!(m.value_of("opt"), Some("myval"));
        /// assert!(m.is_present("opt"));
        /// assert_eq!(m.occurrences_of("opt"), 0);
        /// ```
        pub fn default_value(mut self, val: &'a str) -> Self {
            self.setb(ArgSettings::TakesValue);
            self.default_val = Some(val);
            self
        }

        /// When set to `true` the help string will be displayed on the line after the argument and
        /// indented once. This can be helpful for arguments with very long or complex help messages.
        /// This can also be helpful for arguments with very long flag names, or many/long value names.
        ///
        /// **NOTE:** To apply this setting to all arguments consider using `AppSettings::NextLineHelp`
        ///
        /// # Examples
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// let m = App::new("nlh")
        ///     .arg(Arg::with_name("opt")
        ///         .long("long-option-flag")
        ///         .short("o")
        ///         .takes_value(true)
        ///         .value_names(&["value1", "value2"])
        ///         .help("Some really long help and complex{n}\
        ///                help that makes more sense to be{n}\
        ///                on a line after the option")
        ///         .next_line_help(true))
        ///     .get_matches_from(vec![
        ///         "nlh", "--help"
        ///     ]);
        /// ```
        ///
        /// The above example displays the following help message
        ///
        /// ```ignore
        /// nlh
        ///
        /// USAGE:
        ///     nlh [FLAGS] [OPTIONS]
        ///
        /// FLAGS:
        ///     -h, --help       Prints help information
        ///     -V, --version    Prints version information
        ///
        /// OPTIONS:
        ///     -o, --long-option-flag <value1> <value2>
        ///         Some really long help and complex
        ///         help that makes more sense to be
        ///         on a line after the option
        /// ```
        pub fn next_line_help(mut self, nlh: bool) -> Self {
            if nlh {
                self.setb(ArgSettings::NextLineHelp);
            } else {
                self.unsetb(ArgSettings::NextLineHelp);
            }
            self
        }

        /// Allows custom ordering of args within the help message. Args with a lower value will be
        /// displayed first in the help message. This is helpful when one would like to emphasise
        /// frequently used args, or prioritize those towards the top of the list. Duplicate values
        /// **are** allowed. Args with duplicate display orders will be displayed in alphabetical
        /// order.
        ///
        /// **NOTE:** The default is 999 for all arguments.
        ///
        /// **NOTE:** This setting is ignored for positional arguments which are always displayed in
        /// index order.
        ///
        /// # Examples
        ///
        /// ```rust
        /// # use clap::{App, Arg};
        /// let m = App::new("cust-ord")
        ///     .arg(Arg::with_name("a") // Typically args are grouped alphabetically by name.
        ///                              // Args without a display_order have a value of 999 and are
        ///                              // displayed alphabetically with all other 999 valued args.
        ///         .long("long-option")
        ///         .short("o")
        ///         .takes_value(true)
        ///         .help("Some help and text"))
        ///     .arg(Arg::with_name("b")
        ///         .long("other-option")
        ///         .short("O")
        ///         .takes_value(true)
        ///         .display_order(1)   // In order to force this arg to appear *first*
        ///                             // all we have to do is give it a value lower than 999.
        ///                             // Any other args with a value of 1 will be displayed
        ///                             // alphabetically with this one...then 2 values, then 3, etc.
        ///         .help("I should be first!"))
        ///     .get_matches_from(vec![
        ///         "cust-ord", "--help"
        ///     ]);
        /// ```
        ///
        /// The above example displays the following help message
        ///
        /// ```ignore
        /// cust-ord
        ///
        /// USAGE:
        ///     cust-ord [FLAGS] [OPTIONS]
        ///
        /// FLAGS:
        ///     -h, --help       Prints help information
        ///     -V, --version    Prints version information
        ///
        /// OPTIONS:
        ///     -O, --other-option <b>    I should be first!
        ///     -o, --long-option <a>     Some help and text
        /// ```
        pub fn display_order(mut self, ord: usize) -> Self {
            self.disp_ord = ord;
            self
        }

        /// Checks if one of the `ArgSettings` settings is set for the argument
        pub fn is_set(&self, s: ArgSettings) -> bool {
            self.settings.is_set(s)
        }

        /// Sets one of the `ArgSettings` settings for the argument
        pub fn set(mut self, s: ArgSettings) -> Self {
            self.setb(s);
            self
        }

        /// Unsets one of the `ArgSettings` settings for the argument
        pub fn unset(mut self, s: ArgSettings) -> Self {
            self.unsetb(s);
            self
        }

        #[doc(hidden)]
        pub fn setb(&mut self, s: ArgSettings) {
            self.settings.set(s);
        }

        #[doc(hidden)]
        pub fn unsetb(&mut self, s: ArgSettings) {
            self.settings.unset(s);
        }
    }

    impl<'a, 'b, 'z> From<&'z Arg<'a, 'b>>
        for Arg<'a, 'b> {
        fn from(a: &'z Arg<'a, 'b>) -> Self {
            Arg {
                name: a.name,
                short: a.short,
                long: a.long,
                help: a.help,
                index: a.index,
                possible_vals: a.possible_vals.clone(),
                blacklist: a.blacklist.clone(),
                requires: a.requires.clone(),
                num_vals: a.num_vals,
                min_vals: a.min_vals,
                max_vals: a.max_vals,
                val_names: a.val_names.clone(),
                group: a.group,
                validator: a.validator.clone(),
                overrides: a.overrides.clone(),
                settings: a.settings,
                val_delim: a.val_delim,
                default_val: a.default_val,
                disp_ord: a.disp_ord,
                r_unless: a.r_unless.clone(),
            }
        }
    }

    impl<'a, 'b> Clone for Arg<'a, 'b> {
        fn clone(&self) -> Self {
            Arg {
                name: self.name,
                short: self.short,
                long: self.long,
                help: self.help,
                index: self.index,
                possible_vals: self.possible_vals.clone(),
                blacklist: self.blacklist.clone(),
                requires: self.requires.clone(),
                num_vals: self.num_vals,
                min_vals: self.min_vals,
                max_vals: self.max_vals,
                val_names: self.val_names.clone(),
                group: self.group,
                validator: self.validator.clone(),
                overrides: self.overrides.clone(),
                settings: self.settings,
                val_delim: self.val_delim,
                default_val: self.default_val,
                disp_ord: self.disp_ord,
                r_unless: self.r_unless.clone(),
            }
        }
    }

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