Rework Complex Union Type Example

Hail the Optional monad... Kind of 🤡

Author: swissmanu

examples/04-complex-union-types/complex-union-types.test.ts

@@ -0,0 +1,33 @@
+import { Some, None, Optional } from './more-complex-types';
+const noop = () => {};
+
+describe('More Complex Types: OptionalPattern', () => {
+ it('should match a Some with Some(value)', () => {
+ const someSpy = jest.fn();
+ const noneSpy = jest.fn();
+ const value = 'I have a value';
+ const optional: Optional<string> = new Some(value);
+
+ optional.match({
+ Some: someSpy,
+ None: noneSpy
+ });
+
+ expect(someSpy).toHaveBeenCalledWith(value);
+ expect(noneSpy).not.toHaveBeenCalled();
+ });
+
+ it('should match a None with None()', () => {
+ const someSpy = jest.fn();
+ const noneSpy = jest.fn();
+ const optional: Optional<string> = new None<string>();
+
+ optional.match({
+ Some: someSpy,
+ None: noneSpy
+ });
+
+ expect(someSpy).not.toHaveBeenCalled();
+ expect(noneSpy).toHaveBeenCalled();
+ });
+});

examples/04-complex-union-types/complex-union-types.ts

@@ -0,0 +1,24 @@
+export type Optional<T> = Some<T> | None<T>;
+
+interface OptionalPattern<T> {
+ Some: (d: T) => T;
+ None: () => T;
+}
+
+interface OptionalMatcher {
+ match<T>(p: OptionalPattern<T>): T;
+}
+
+export class Some<T> implements OptionalMatcher {
+ constructor(private readonly value: T) {}
+
+ match(p: OptionalPattern<T>): T {
+ return p.Some(this.value);
+ }
+}
+
+export class None<T> implements OptionalMatcher {
+ match(p: OptionalPattern<T>): T {
+ return p.None();
+ }
+}