Added another exercise

Author: mattpocock

src/04-generics-advanced/20.5-spotting-missing-generics.problem.ts

@@ -0,0 +1,23 @@
+import { Equal, Expect } from "../helpers/type-utils";
+
+const getValue = <TObj>(obj: TObj, key: keyof TObj) => {
+  return obj[key];
+};
+
+const obj = {
+  a: 1,
+  b: "some-string",
+  c: true,
+};
+
+const numberResult = getValue(obj, "a");
+const stringResult = getValue(obj, "b");
+const booleanResult = getValue(obj, "c");
+
+type tests = [
+  Expect<Equal<typeof numberResult, number>>,
+  Expect<Equal<typeof stringResult, string>>,
+  Expect<Equal<typeof booleanResult, boolean>>,
+];
+
+export {};

src/04-generics-advanced/20.5-spotting-missing-generics.solution.ts

@@ -0,0 +1,23 @@
+import { Equal, Expect } from "../helpers/type-utils";
+
+const getValue = <TObj, TKey extends keyof TObj>(obj: TObj, key: TKey) => {
+  return obj[key];
+};
+
+const obj = {
+  a: 1,
+  b: "some-string",
+  c: true,
+};
+
+const numberResult = getValue(obj, "a");
+const stringResult = getValue(obj, "b");
+const booleanResult = getValue(obj, "c");
+
+type tests = [
+  Expect<Equal<typeof numberResult, number>>,
+  Expect<Equal<typeof stringResult, string>>,
+  Expect<Equal<typeof booleanResult, boolean>>,
+];
+
+export {};