Add UnionToTuple type

index.d.ts

@@ -86,6 +86,7 @@ export type {WritableKeysOf} from './source/writable-keys-of';
 export type {HasWritableKeys} from './source/has-writable-keys';
 export type {Spread} from './source/spread';
 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

@@ -247,6 +247,7 @@ 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 a tuple type of its elements.
 
 ### Numeric
 

source/union-to-tuple.d.ts

@@ -0,0 +1,30 @@
+import type {UnionToIntersection} from './union-to-intersection';
+
+/**
+ Convert a union type into a tuple/array 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
+ ```
+ 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<Tuple> = UnionToIntersection<
+Tuple extends never ? never : (_: Tuple) => Tuple
+> extends (_: never) => infer LastTupleElement
+	? [...UnionToTuple<Exclude<Tuple, LastTupleElement>>, LastTupleElement]
+	: [];

test-d/union-to-tuple.ts

@@ -0,0 +1,12 @@
+import {expectAssignable, expectError, expectType} from 'tsd';
+import type {UnionToTuple} from '../index';
+
+type Options = UnionToTuple<'a' | 'b' | 'c'>;
+
+const options: Options = ['a', 'b', 'c'];
+
+expectAssignable<Options>(options);
+expectType<'a'>(options[0]);
+expectType<'b'>(options[1]);
+expectType<'c'>(options[2]);
+expectError(options[0] = 'b');