feat(extract): add pattern matching for option

operators/extract.ts

@@ -111,3 +111,36 @@ export function expect<T>(
 
   throw new error(msg);
 }
+
+/** {@link Option} matcher. */
+export interface Matcher<T, U> {
+  /** Match on `Some`. */
+  Some: (value: T) => U;
+
+  /** Match on `None`. */
+  None: () => U;
+}
+
+/** Pattern matching for {@link option}. Match on {@link matcher.Some} if `Some`, otherwise match on {@link matcher.None}.
+ *
+ * @example
+ * ```ts
+ * import { None, type Option } from "https://deno.land/x/optio/spec.ts";
+ * import { match } from "https://deno.land/x/optio/operators/extract.ts";
+ *
+ * declare const option: Option<number>;
+ *
+ * match(option, {
+ *  Some: (value) => value,
+ *  None: () => 500,
+ * });
+ * ```
+ */
+export function match<T, U>(
+  option: Option<T>,
+  matcher: Readonly<Matcher<T, U>>,
+): U {
+  if (isSome(option)) return matcher.Some(option.get);
+
+  return matcher.None();
+}

operators/extract_test.ts

@@ -1,10 +1,10 @@
 // Copyright © 2023 Tomoki Miyauchi. All rights reserved. MIT license.
-// This module is browser compatible.
 
-import { expect, unwrap, unwrapOr, unwrapOrElse } from "./extract.ts";
+import { expect, match, unwrap, unwrapOr, unwrapOrElse } from "./extract.ts";
 import { None, Some } from "../spec.ts";
 import {
   assertEquals,
+  assertSpyCallArgs,
   assertSpyCalls,
   assertThrows,
   describe,
@@ -61,3 +61,24 @@ describe("expect", () => {
     assertThrows(() => expect(None, message, RangeError), RangeError, message);
   });
 });
+
+describe("match", () => {
+  it("should call Some if Some", () => {
+    const s = spy(() => 1);
+    const n = spy(() => 2);
+
+    assertEquals(match(Some.of(0), { Some: s, None: n }), 1);
+    assertSpyCalls(s, 1);
+    assertSpyCalls(n, 0);
+    assertSpyCallArgs(s, 0, [0]);
+  });
+
+  it("should call None if None", () => {
+    const s = spy(() => 1);
+    const n = spy(() => 2);
+
+    assertEquals(match(None, { Some: s, None: n }), 2);
+    assertSpyCalls(s, 0);
+    assertSpyCalls(n, 1);
+  });
+});