Macro clap::value_t

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

Convenience macro getting a typed value T where T implements std::str::FromStr This macro returns a Result<T,String> which allows you as the developer to decide what you’d like to do on a failed parse. There are two types of errors, parse failures and those where the argument wasn’t present (such as a non-required argument).

You can use it to get a single value, or a Vec<T> with the values_of()

NOTE: Be cautious, as since this a macro invocation it’s not exactly like standard syntax.

Example single value

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!(matches.value_of("length"), u32)
                .unwrap_or_else(|e|{
                    println!("{}",e);
                    std::process::exit(1)
                });

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

Example multiple values

let matches = App::new("myapp")
              .arg_from_usage("[seq]... 'A sequence of pos whole nums, i.e. 20 45'")
              .get_matches();
for v in value_t!(matches.values_of("seq"), u32)
            .unwrap_or_else(|e|{
                println!("{}",e);
                std::process::exit(1)
            }) {
    println!("{} + 2: {}", v, v + 2);
}