Macro arg

macro_rules! arg {
    (-- $($long:ident)-+ | - $short:ident) => { ... };
    (- $short:ident | -- $($long:ident)-+) => { ... };
    (-- $($a:ident)-+) => { ... };
    (- $a:ident) => { ... };
    ($a:literal) => { ... };
    (+ $first:ident) => { ... };
    (+ $first:ident - $($next:ident)-+) => { ... };
}

Quick way to contruct Arguments. Supports long and short arguments by prepending one or two dashes, or “bare” arguments that aren’t classified as either long or short.

Long arguments support anything Rust considers an “identifier” (variable name), separated by at most one dash. For example arg!(--long) or arg!(--long-arg) are valid, but arg!(--long--arg) isn’t.

Short arguments must only be one character long (eg. arg!(-a)). This requirement isn’t checked due to limitations of macro_rules, and I’m not writing an entire proc macro crate for one shortcut.
If you use more than one character, it won’t ever be matched.

In a match block, you can “or” exactly one long and short argument like arg!(-h | --help), which is equivalent to arg!(-h) | arg!(--help).

Bare arguments (anything not valid as a long or short) must be quoted, for example arg!("bare-argument"). Putting one or two dashes in front of the argument will never match as it’d be recognized as a valid argument, but three would be parsed as a bare (eg. arg!("---lol")).

The arg!(+...) syntax is used internally to combine Rust identifiers separated by dashes.