Aliasing

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.

1. // `NanoSecond` is a new name for `u64`.
2. type NanoSecond = u64;
3. type Inch = u64;

5. // Use an attribute to silence warning.
6. #[allow(non_camel_case_types)]
7. type u64_t = u64;
8. // TODO ^ Try removing the attribute

10. fn main() {
11. // `NanoSecond` = `Inch` = `u64_t` = `u64`.
12. let nanoseconds: NanoSecond = 5 as u64_t;
13. let inches: Inch = 2 as u64_t;

15. // Note that type aliases *don't* provide any extra type safety, because
16. // aliases are *not* new types
17. println!("{} nanoseconds + {} inches = {} unit?",
18. nanoseconds,
19. inches,
20. nanoseconds + inches);
21. }

The main use of aliases is to reduce boilerplate; for example the IoResult<T> type is an alias for the Result<T, IoError> type.

See also:

Attributes