Trait MatchArg 

pub trait MatchArg:
    Sized
    + Copy
    + 'static {
    const CHOICES: &'static [&'static str];
    const ALIASES: &'static [MatchArgAlias] = _;

    // Required methods
    fn from_choice(choice: &str) -> Option<Self>;
    fn to_choice(self) -> &'static str;
}

Trait for enum types that support match.arg-style string conversion.

Implementors provide a fixed set of choice strings and bidirectional conversion between enum variants and their string representations.

Use #[derive(MatchArg)] to auto-generate this implementation.

Required Associated Constants

const CHOICES: &'static [&'static str]

The canonical choice strings, in variant declaration order.

The first choice is the default when the R argument is NULL.

Provided Associated Constants

const ALIASES: &'static [MatchArgAlias] = _

Other spellings of a choice: MatchArgAlias::new("grey", "gray") lets a user write "grey" for the choice "gray" (#1843).

An alias selects its choice only when typed in full: a prefix matches the choices alone, so "gr" stays the prefix of "gray" it was. Every matcher reads it, the generated wrapper’s check and the Rust side alike (match_arg_from_sexp, match_arg_param, match_arg_vec_from_sexp element by element, the Either arm).

Every error that lists the choices names the listed aliases after them, 'color' should be one of "red", "gray", "blue" (or "grey" for "gray"), on both sides (#2148). An alias built with MatchArgAlias::unlisted is matched the same way and named by no error. The R formal, the usage and the @param line list CHOICES only.

#[derive(MatchArg)] fills it from #[match_arg(alias = "...")] on a variant (listed = false for an unlisted one). A hand-written impl lists its aliases here, not in from_choice, which the R-side check never reaches. The wrappers writer refuses, for a type used as a match_arg parameter, an alias that is empty, "NA", a choice, repeated, or a prefix of a choice other than its own, and a target that is not a choice.

Required Methods

fn from_choice(choice: &str) -> Option<Self>

Convert a choice string to the corresponding enum variant.

Returns None if the string doesn’t match any choice exactly. An alias is not a choice: ALIASES maps it.

fn to_choice(self) -> &'static str

Convert the enum variant to its canonical choice string.

Dyn Compatibility

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety".

Implementors