Type aliases

TypeAlias :
   type IDENTIFIER GenericParams? ( : TypeParamBounds )? WhereClause? ( = Type )? ;

A type alias defines a new name for an existing type. Type aliases are declared with the keyword type. Every value has a single, specific type, but may implement several different traits, or be compatible with several different type constraints.

For example, the following defines the type Point as a synonym for the type (u8, u8), the type of pairs of unsigned 8 bit integers:

fn main() {
type Point = (u8, u8);
let p: Point = (41, 68);

A type alias to a tuple-struct or unit-struct cannot be used to qualify that type's constructor:

fn main() {
struct MyStruct(u32);

use MyStruct as UseAlias;
type TypeAlias = MyStruct;

let _ = UseAlias(5); // OK
let _ = TypeAlias(5); // Doesn't work

A type alias without the Type specification may only appear as an associated type in a trait.

A type alias with TypeParamBounds may only specified when used as an associated type in a trait.