Macro value_t_or_exit

macro_rules! value_t_or_exit {
    ($m:ident, $v:expr, $t:ty) => { ... };
    ($m:ident.value_of($v:expr), $t:ty) => { ... };
}

Convenience macro getting a typed value T where T implements std::str::FromStr or exiting upon error, instead of returning a Result type.

NOTE: This macro is for backwards compatibility sake. Prefer value_t!(/* ... */).unwrap_or_else(|e| e.exit())

Examples

let matches = App::new("myapp")
              .arg_from_usage("[length] 'Set the length to use as a pos whole num, i.e. 20'")
              .get_matches();

let len      = value_t_or_exit!(matches.value_of("length"), u32);
let also_len = value_t_or_exit!(matches, "length", u32);

println!("{} + 2: {}", len, len + 2);