feat: improve result and options types

packages/result/src/lib/Option.ts

@@ -224,7 +224,8 @@ export class Option<T, Exists extends boolean = boolean> {
 	 *
 	 * @see {@link https://doc.rust-lang.org/std/option/enum.Option.html#method.map}
 	 */
-	public map<U>(cb: (value: T) => U): If<Exists, Some<U>, None> {
+	public map<U>(cb: (value: T) => U): Option<U, Exists> {
+		// @ts-expect-error Complex types
 		return this.match({ some: (value) => some(cb(value)), none: returnThis });
 	}
 
@@ -250,7 +251,8 @@ export class Option<T, Exists extends boolean = boolean> {
 	 *
 	 * @note This is an extension not supported in Rust
 	 */
-	public mapInto<OutputOption extends AnyOption>(cb: (value: T) => OutputOption): If<Exists, OutputOption, None> {
+	public mapInto<OutputOption extends AnyOption>(cb: (value: T) => OutputOption): OutputOption {
+		// @ts-expect-error Complex types
 		return this.match({ some: (value) => cb(value), none: returnThis });
 	}
 
@@ -504,7 +506,8 @@ export class Option<T, Exists extends boolean = boolean> {
 	 *
 	 * @see {@link https://doc.rust-lang.org/std/result/enum.Result.html#method.and_then}
 	 */
-	public andThen<OutputOption extends AnyOption>(cb: (value: T) => OutputOption): If<Exists, OutputOption, None> {
+	public andThen<OutputOption extends AnyOption>(cb: (value: T) => OutputOption): OutputOption {
+		// @ts-expect-error Complex types
 		return this.match({ some: (value) => cb(value), none: returnThis });
 	}
 

packages/result/src/lib/Result.ts

@@ -707,7 +707,8 @@ export class Result<T, E, const Success extends boolean = boolean> {
 	 *
 	 * @see {@link https://doc.rust-lang.org/std/result/enum.Result.html#method.and_then}
 	 */
-	public andThen<OutputResult extends AnyResult>(cb: (value: T) => OutputResult): If<Success, OutputResult, Err<E>> {
+	public andThen<OutputResult extends AnyResult>(cb: (value: T) => OutputResult): OutputResult {
+		// @ts-expect-error Complex types
 		return this.match({ ok: (value) => cb(value), err: returnThis });
 	}
 

packages/result/tests/Option.test.ts

@@ -174,6 +174,15 @@ describe('Option', () => {
 				expect<None>(x.map(op)).toBe(none);
 				expect(op).not.toHaveBeenCalled();
 			});
+
+			test('GIVEN option THEN chain map THEN Return Option<string>', () => {
+				const x = Option.from(5);
+				const cb = vi.fn((value: number) => `${value}`);
+				const mapChain = x.map(cb);
+
+				expectTypeOf(mapChain).toMatchTypeOf<Option<string>>();
+				expect<Option<string>>(mapChain).toEqual(some('5'));
+			});
 		});
 
 		describe('mapInto', () => {
@@ -191,7 +200,7 @@ describe('Option', () => {
 				const x = none;
 				const op = vi.fn((value: string) => some(value.length));
 
-				expect<None>(x.mapInto(op)).toBe(none);
+				expect(x.mapInto(op)).toBe(none);
 				expect(op).not.toHaveBeenCalled();
 			});
 		});
@@ -406,9 +415,18 @@ describe('Option', () => {
 				const x = none;
 				const op = vi.fn(cb);
 
-				expect<typeof x>(x.andThen(op)).toBe(none);
+				expect(x.andThen(op)).toBe(none);
 				expect(op).not.toHaveBeenCalled();
 			});
+
+			test('GIVEN option THEN andThen and chain map THEN Return Option<number>', () => {
+				const x = Option.from(5);
+				const cb = vi.fn((value: number) => some(`${value}`));
+				const mapChain = x.andThen(cb).map((value) => Number(value));
+
+				expectTypeOf(mapChain).toMatchTypeOf<Option<number>>();
+				expect<Option<number>>(mapChain).toEqual(some(5));
+			});
 		});
 
 		describe('or', () => {

packages/result/tests/Result.test.ts

@@ -533,9 +533,18 @@ describe('Result', () => {
 				const x = err('not a number');
 				const op = vi.fn(cb);
 
-				expect<typeof x>(x.andThen(op)).toBe(x);
+				expect(x.andThen(op)).toBe(x);
 				expect(op).not.toHaveBeenCalled();
 			});
+
+			test('GIVEN ok THEN chain andThen and map THEN returns Ok<number, string>', () => {
+				const x = Result.from<number, Error>(1);
+				const cb = vi.fn((value: number) => ok(`${value}`));
+				const mapChain = x.andThen(cb).map((value) => Number(value));
+
+				expectTypeOf(mapChain).toMatchTypeOf<Result<number, string>>();
+				expect<Result<number, string>>(mapChain).toEqual(ok(1));
+			});
 		});
 
 		describe('or', () => {