feat(typescript-types): Add Assign<Shape,Defaults,Obj>

packages/typescript-types/README.md

@@ -27,3 +27,11 @@ The types included in this library are categorized by their purpose.
 | [`OptionalKeysOf<T>`][] | A union of all keys of `T` that are marked as optional. If `T` is a union, a union of the optional keys of all union members of `T` is returned. |
 
 [`OptionalKeysOf<T>`]: src/optional-keys-of.ts
+
+#### Combination Types
+
+| Type                               | Description                                                                                                             |
+| ---------------------------------- | ----------------------------------------------------------------------------------------------------------------------- |
+| [`Assign<Shape, Defaults, Obj>`][] | Return a type with the structure of `Shape` and value types from `Obj` or `Default` for missing optional keys in `Obj`. |
+
+[`Assign<Shape, Defaults, Obj>`]: src/assign.ts

packages/typescript-types/src/assign.ts

@@ -0,0 +1,9 @@
+import type { OptionalKeysOf } from './optional-keys-of.js'
+
+export type Assign<
+	Shape extends object,
+	Defaults extends Pick<Required<Shape>, OptionalKeysOf<Shape>>,
+	Obj extends Shape
+> = {
+	[K in keyof Shape]: K extends keyof Obj ? Obj[K] : K extends keyof Defaults ? Defaults[K] : never
+}

packages/typescript-types/test/assign.tst.ts

@@ -0,0 +1,29 @@
+import type { Assign } from '@/assign.js'
+import { expect } from 'tstyche'
+
+interface Person {
+	name: string
+	age?: number
+}
+
+interface Options extends Person {
+	relations?: Array<Person>
+}
+
+interface DefaultValues {
+	name: 'Max Mustermann'
+	age: 17
+	relations: []
+}
+
+expect<Assign<Options, DefaultValues, { name: 'Another Name' }>>().type.toBe<{
+	name: 'Another Name'
+	age?: 17
+	relations?: []
+}>()
+
+expect<Assign<Options, DefaultValues, { name: 'Another Name'; age: 18 }>>().type.toBe<{
+	name: 'Another Name'
+	age?: 18
+	relations?: []
+}>()