type语句声明可以以现有类型被用来给一个新的名字。类型必须有 CamelCase 名称, 或者编译器会提出警告。例外(异常)是原始类型： usize,f32, 等.
// `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
// Use an attribute to silence warnings
#[allow(trivial_numeric_casts)]
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);
}
使用别名主要是减少输入;例如 IoResult<T> 是类型Result<T, IoError> 的别名.
