feat/solution-17: solution without type casts

src/04-generics-advanced/17-you-say-goodbye-i-say-hello.solution.3.ts

@@ -0,0 +1,26 @@
+import { expect, it } from "vitest";
+import { Equal, Expect } from "../helpers/type-utils";
+
+function youSayGoodbyeISayHello(greeting: 'hello'): 'goodbye'
+function youSayGoodbyeISayHello(greeting: 'goodbye'): 'hello'
+function youSayGoodbyeISayHello<TGreeting extends "hello" | "goodbye">(
+  greeting: TGreeting
+){
+  return greeting === "goodbye" ? "hello" : "goodbye";
+}
+
+it("Should return goodbye when hello is passed in", () => {
+  const result = youSayGoodbyeISayHello("hello");
+
+  type test = [Expect<Equal<typeof result, "goodbye">>];
+
+  expect(result).toEqual("goodbye");
+});
+
+it("Should return hello when goodbye is passed in", () => {
+  const result = youSayGoodbyeISayHello("goodbye");
+
+  type test = [Expect<Equal<typeof result, "hello">>];
+
+  expect(result).toEqual("hello");
+});