Add UnionToTuple type (#945)

Co-authored-by: Sindre Sorhus <sindresorhus@gmail.com>

index.d.ts

@@ -104,6 +104,7 @@ export type {Spread} from './source/spread';
 export type {IsInteger} from './source/is-integer';
 export type {IsFloat} from './source/is-float';
 export type {TupleToUnion} from './source/tuple-to-union';
+export type {UnionToTuple} from './source/union-to-tuple';
 export type {IntRange} from './source/int-range';
 export type {IsEqual} from './source/is-equal';
 export type {

readme.md

@@ -283,6 +283,7 @@ type ShouldBeNever = IfAny<'not any', 'not never', 'never'>;
 - [`MultidimensionalReadonlyArray`](source/multidimensional-readonly-array.d.ts) - Create a type that represents a multidimensional readonly array of the given type and dimensions.
 - [`ReadonlyTuple`](source/readonly-tuple.d.ts) - Create a type that represents a read-only tuple of the given type and length.
 - [`TupleToUnion`](source/tuple-to-union.d.ts) - Convert a tuple/array into a union type of its elements.
+- [`UnionToTuple`](source/union-to-tuple.d.ts) - Convert a union type into an unordered tuple type of its elements.
 
 ### Numeric
 

source/union-to-tuple.d.ts

@@ -0,0 +1,54 @@
+import type {IsNever} from './is-never';
+import type {UnionToIntersection} from './union-to-intersection';
+
+/**
+Returns the last element of a union type.
+
+@example
+```
+type Last = LastOfUnion<1 | 2 | 3>;
+//=> 3
+```
+*/
+type LastOfUnion<T> =
+UnionToIntersection<T extends any ? () => T : never> extends () => (infer R)
+	? R
+	: never;
+
+/**
+Convert a union type into an unordered tuple type of its elements.
+
+This can be useful when you have objects with a finite set of keys and want a type defining only the allowed keys, but do not want to repeat yourself.
+
+@example
+```
+import type {UnionToTuple} from 'type-fest';
+
+type Numbers = 1 | 2 | 3;
+type NumbersTuple = UnionToTuple<Numbers>;
+//=> [1, 2, 3]
+```
+
+@example
+```
+import type {UnionToTuple} from 'type-fest';
+
+const pets = {
+  dog: '🐶',
+  cat: '🐱',
+  snake: '🐍',
+};
+
+type Pet = keyof typeof pets;
+//=> 'dog' | 'cat' | 'snake'
+
+const petList = Object.keys(pets) as UnionToTuple<Pet>;
+//=> ['dog', 'cat', 'snake']
+```
+
+@category Array
+*/
+export type UnionToTuple<T, L = LastOfUnion<T>> =
+IsNever<T> extends false
+	? [...UnionToTuple<Exclude<T, L>>, L]
+	: [];

test-d/union-to-tuple.ts

@@ -0,0 +1,13 @@
+import {expectAssignable, expectError, expectType} from 'tsd';
+import type {UnionToTuple} from '../index';
+
+type Options = UnionToTuple<'a' | 'b' | 'c'>;
+// Results unordered
+expectAssignable<['a', 'b', 'c'] | ['a', 'c', 'b'] | ['b', 'a', 'c'] | ['b', 'c', 'a'] | ['c', 'a', 'b'] | ['c', 'b', 'a']>({} as Options);
+expectType<Options[number]>({} as ('a' | 'b' | 'c'));
+
+type Options1 = UnionToTuple<1 | 2 | 3>;
+expectType<Options1[number]>({} as (1 | 2 | 3));
+
+type Options2 = UnionToTuple<boolean | 1>;
+expectType<Options2[number]>({} as (1 | false | true));