match

Compares a value against patterns and evaluates the first arm that matches.

Arms are pattern => expression separated by commas. Patterns can be enum variants (with nested payload patterns), integer literals, bindings, and _ inside a payload. The arms must cover every case; default => catches the rest. match is an expression, so it yields a value.

fn label(Option<int> code) -> string {
    return match code {
        Option::Some(200) => "ok",
        Option::Some(_) => "other",
        Option::None => "none",
    };
}

See also#

• fn: Declares a function, a method, or (written in an expression) an anonymous function.
• let: Declares a mutable local variable.
• const: Declares a binding that cannot be reassigned: a local, a module constant, or a class field that is set only by new.
• static: Declares a module-level or class-level slot shared by the whole program, or a method without self.
• readonly: A read-only view of a value: nothing reachable through it can be changed.
• if: Runs a block when a bool condition is true.
• else: Introduces the branch of an if that runs when its condition is false (or its pattern does not match).
• while: Repeats a block while a bool condition is true.