Aliasing

The type statement can be used to give a new name to an existing type. Types must have UpperCamelCase names, or the compiler will raise a warning. The exception to this rule are the primitive types: usize, f32, etc.

// `NanoSecond`, `Inch`, and `U64` are new names for `u64`.
type NanoSecond = u64;
type Inch = u64;
type U64 = u64;

fn main() {
    // `NanoSecond` = `Inch` = `U64` = `u64`.
    let nanoseconds: NanoSecond = 5_u64;
    let inches: Inch = 2_u64;

    // Note that type aliases *don't* provide any extra type safety, because
    // aliases are *not* new types
    println!("{} nanoseconds + {} inches = {} unit?", nanoseconds, inches, nanoseconds + inches);
}

The main use of aliases is to reduce boilerplate; for example the SyscallResult<T> type is an alias for the Result<(), Error> type.

See also:

Attributes