Type aliases

Use alias to introduce another name for a type:

alias UserId = Int;
alias DisplayName = String;

The alias can be used in declarations and function signatures:

fun loadUser(id: UserId) {
    println("Loading user " + toString(id));
}

var id: UserId = 42;
loadUser(id);

Alias identity

An alias does not create a distinct type. The alias and its target remain interchangeable:

alias Score = Int;

var score: Score = 10;
var number: Int = score;

Use an alias to improve vocabulary or shorten a long type name. Do not use one when the compiler must prevent values from different domains from mixing.

Public aliases

Export an alias from a module with pub:

pub alias RequestId = UInt64;

Callers can then import it like any other public declaration.