Create 00191-medium-append-args.ts

Author: programandoconro

Languages/Typescript/Generics/00191-medium-append-args.ts

@@ -0,0 +1,62 @@
+/*
+  191 - Append Argument
+  -------
+  by Maciej Sikora (@maciejsikora) #medium #arguments
+
+  ### Question
+
+  For given function type `Fn`, and any type `A` (any in this context means we don't restrict the type, and I don't have in mind any type 😉) create a generic type which will take `Fn` as the first argument, `A` as the second, and will produce function type `G` which will be the same as `Fn` but with appended argument `A` as a last one.
+
+  For example,
+
+  ```typescript
+  type Fn = (a: number, b: string) => number
+
+  type Result = AppendArgument<Fn, boolean>
+  // expected be (a: number, b: string, x: boolean) => number
+  ```
+  > This question is ported from the [original article](https://dev.to/macsikora/advanced-typescript-exercises-question-4-495c) by [@maciejsikora](https://github.com/maciejsikora)
+
+  > View on GitHub: https://tsch.js.org/191
+*/
+
+/* _____________ Your Code Here _____________ */
+// my try
+type AppendArgument<Fn extends (...args: any[]) => unknown, A> = Fn extends (
+  ...args: infer P extends any[]
+) => any
+  ? (...args: [...P, A]) => ReturnType<Fn>
+  : never;
+  
+ // official answer
+type AppendArgument2<Fn extends (...args: any[]) => unknown, A> = (
+  ...args: [...Parameters<Fn>, A]
+) => ReturnType<Fn>;
+
+type Fn = (a: number, b: string) => number;
+
+type Result = AppendArgument<Fn, boolean>;
+//   ^?
+
+/* _____________ Test Cases _____________ */
+import type { Equal, Expect } from "@type-challenges/utils";
+
+type Case1 = AppendArgument<(a: number, b: string) => number, boolean>;
+type Result1 = (a: number, b: string, x: boolean) => number;
+
+type Case2 = AppendArgument<() => void, undefined>;
+type Result2 = (x: undefined) => void;
+
+type cases = [
+  Expect<Equal<Case1, Result1>>,
+  Expect<Equal<Case2, Result2>>,
+  // @ts-expect-error
+  AppendArgument<unknown, undefined>
+];
+
+/* _____________ Further Steps _____________ */
+/*
+  > Share your solutions: https://tsch.js.org/191/answer
+  > View solutions: https://tsch.js.org/191/solutions
+  > More Challenges: https://tsch.js.org
+*/