Rust by Example

5.4 Alias

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

// `NanoSecond` is a new name for `u64` type NanoSecond = u64; type Inch = u64; // Use an attribute to silence warning #[allow(non_camel_case_types)] type u64_t = u64; // TODO ^ Try removing the attribute fn main() { // `NanoSecond` = `Inch` = `u64_t` = `u64` let nanoseconds: NanoSecond = 5 as u64_t; let inches: Inch = 2 as u64_t; // 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 typing; for example the IoResult<T> type is an alias for the Result<T, IoError> type.