Type aliasing

Type aliasing is a feature in some programming languages that allows creating a reference to a type using another name. It does not create a new type hence does not increase type safety. It can be used to shorten a long name. Languages allowing type aliasing include: C++, C# Crystal, D, Dart, Elixir, Elm, F#, Go, Hack, Haskell, Julia, Kotlin, Nim, OCaml, Python, Rust, Scala, Swift and TypeScript.

Example

C++

C++ features type aliasing using the using keyword.

using Distance = int;

C#

C# since version 12 features type aliasing using the using keyword.

using Distance = int;

Crystal

Crystal features type aliasing using the alias keyword.

alias Distance = Int32;

D

D features type aliasing using the alias keyword.

alias Distance = int;

Dart

Dart features type aliasing using the typedef keyword.

typedef Distance = int;

Elixir

Elixir features type aliasing using @type.

@type Distance :: integer

Elm

Elm features type aliasing using type alias.

type alias Distance = Int

F#

F3 features type aliasing using the type keyword.

type Distance = int

Go

Go features type aliasing using the type keyword.

type Distance int

Hack

Hack features type aliasing using the newtype keyword.

newtype Distance = int;

Haskell

Haskell features type aliasing using the type keyword.

type Distance = Int;

Julia

Julia features type aliasing.

const Distance = Int

Kotlin

Kotlin features type aliasing using the typealias keyword.

typealias Distance = Int

Nim

Nim features type aliasing.

type
  Distance* = int

OCaml

OCaml features type aliasing.

type distance = int

Python

Python features type aliasing.

Vector = list[float]

Type aliases may be marked with TypeAlias to make it explicit that the statement is a type alias declaration, not a normal variable assignment.

from typing import TypeAlias

Vector: TypeAlias = list[float]

Rust

Rust features type aliasing using the type keyword.

type Point = (u8, u8);

Scala

Scala can create type aliases using opaque types.

object Logarithms:
  opaque type Logarithm = Double

Swift

Swift features type aliasing using the typealias keyword.

typealias Distance = Int;

TypeScript

TypeScript features type aliasing using the type keyword.

type Distance = number;