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_ (underscore)

The _ keyword is a wildcard/placeholder token. Unlike an ordinary identifier, _ does not bind a name; it signals "match anything" or "discard this value". Because it is a reserved token, it cannot be used as a variable, function, type, or parameter name.

Syntax & Example​

As a catch-all pattern in match:

match n {
    0 => print("zero"),
    _ => print("many"),
}

As a placeholder for unused values:

let _, value = pair;

Use Cases​

  • Writing a catch-all arm in a match expression.
  • Discarding parts of a tuple or struct during destructuring.
  • Marking intentionally unused bindings or parameters.
Not an identifier

_ is lexed as the Underscore token, not as an Identifier. It is a wildcard/placeholder and cannot be used as an ordinary binding name.