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use std::fmt;
use std::option::Option as Optional;
use std::string::String;

/// An argument is a positional parameter. It must come after any Options
/// the command supports, and can have a default value if it is not
/// specified by the user explicitly.
///
/// The final Argument for a Command can be variadic (that is, it can
/// accept more than one value), but whether or not this is the case is a
/// property of the Command, not of the Argument (because the Argument only
/// stores a description of the argument, not its final value).
#[derive(Debug)]
pub struct Argument {
    pub name: String,
    pub help: String,
    pub default_value: Optional<Vec<String>>,
}

impl Argument {
    pub fn new(name: &str, help: &str, default_value: Optional<Vec<String>>) -> Argument {
        Argument {
            name: name.to_owned(),
            help: help.to_owned(),
            default_value: default_value,
        }
    }
}

impl fmt::Display for Argument {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        try!(write!(f, "{} - {}", self.name, self.help));
        if let Some(default) = self.default_value.as_ref() {
            try!(write!(f, " [Default: {}]", &default[..].join(", ")));
        }
        Ok(())
    }
}