Add object, object.empty pattern and tests

Author: gitsunmin

README.md

@@ -1497,7 +1497,7 @@ const fn = (input: string) =>
     .with(P.object.empty(), () => 'Empty!')
     .otherwise(() => 'Full!');
 
-console.log(fn('{}')); // Empty
+console.log(fn({})); // Empty!
 ```
 
 ## Types

src/patterns.ts

@@ -34,6 +34,7 @@ import {
   StringChainable,
   ArrayChainable,
   Variadic,
+  ObjectChainable,
 } from './types/Pattern';
 
 export type { Pattern, Fn as unstable_Fn };
@@ -634,6 +635,12 @@ function isNullish<T>(x: T | null | undefined): x is null | undefined {
   return x === null || x === undefined;
 }
 
+function isObject<T>(x: T | object): x is object {
+  return typeof x === 'object' &&
+  !Array.isArray(x) &&
+  x !== null
+}
+
 type AnyConstructor = abstract new (...args: any[]) => any;
 
 function isInstanceOf<T extends AnyConstructor>(classConstructor: T) {
@@ -1110,3 +1117,35 @@ export function shape<input, const pattern extends Pattern<input>>(
 export function shape(pattern: UnknownPattern) {
   return chainable(when(isMatching(pattern)));
 }
+
+/**
+ * `P.object.empty()` is a pattern, matching **objects** with no keys.
+ *
+ * [Read the documentation for `P.object.empty` on GitHub](https://github.com/gvergnaud/ts-pattern#pobjectempty)
+ *
+ * @example
+ *  match(value)
+ *   .with(P.object.empty(), () => 'will match on empty objects')
+ */
+const emptyObject = <input>(): GuardExcludeP<input, object, never> => when(
+    (value) => value && typeof value === 'object' && Object.keys(value).length === 0,
+  );
+
+const objectChainable = <pattern extends Matcher<any, any, any, any, any>>(
+  pattern: pattern
+): ObjectChainable<pattern> =>
+  Object.assign(chainable(pattern), {
+    empty: () => objectChainable(intersection(pattern, emptyObject())),
+  }) as any;
+
+/**
+ * `P.object` is a wildcard pattern, matching any **object**.
+ * It lets you call methods like `.empty()`, `.and`, `.or` and `.select()`
+ * On structural patterns, like objects and arrays.
+ * [Read the documentation for `P.object` on GitHub](https://github.com/gvergnaud/ts-pattern#pobject-predicates)
+ * 
+ * @example 
+ * match(value)
+ *  .with(P.object.empty(), () => 'will match on empty objects')
+ **/
+export const object: ObjectChainable<any> = objectChainable(when(isObject));

src/types/Pattern.ts

@@ -15,6 +15,7 @@ export type MatcherType =
   | 'or'
   | 'and'
   | 'array'
+  | 'object'
   | 'map'
   | 'set'
   | 'select'
@@ -97,6 +98,8 @@ export type CustomP<input, pattern, narrowedOrFn> = Matcher<
 
 export type ArrayP<input, p> = Matcher<input, p, 'array'>;
 
+export type ObjectP<input, p> = Matcher<input, p, 'object'>;
+
 export type OptionalP<input, p> = Matcher<input, p, 'optional'>;
 
 export type MapP<input, pkey, pvalue> = Matcher<input, [pkey, pvalue], 'map'>;
@@ -191,7 +194,6 @@ export type NullishPattern = Chainable<
   GuardP<unknown, null | undefined>,
   never
 >;
-
 type MergeGuards<input, guard1, guard2> = [guard1, guard2] extends [
   GuardExcludeP<any, infer narrowed1, infer excluded1>,
   GuardExcludeP<any, infer narrowed2, infer excluded2>
@@ -658,3 +660,26 @@ export type ArrayChainable<
     },
     omitted
   >;
+
+export type ObjectChainable<
+  pattern,
+  omitted extends string = never
+> = Chainable<pattern, omitted> &
+  Omit<
+    {
+      /**
+       * `.empty()` matches an empty object.
+       *
+       * [Read the documentation for `P.object.empty` on GitHub](https://github.com/gvergnaud/ts-pattern#pobjectempty)
+       *
+       * @example
+       * match(value)
+       *  .with(P.object.empty(), () => 'empty object')
+       */
+      empty<input>(): ObjectChainable<
+        ObjectP<input, Record<string, never>>,
+        omitted | 'empty'
+      >;
+    },
+    omitted
+  >;

tests/object.test.ts

@@ -0,0 +1,80 @@
+import { Expect, Equal } from '../src/types/helpers';
+import { P, match } from '../src';
+
+describe('Object', () => {
+  it('should match exact object', () => {
+    const fn = () => 'hello';
+
+    const res = match({ str: fn() })
+      .with({ str: 'world' }, (obj) => {
+        type t = Expect<Equal<typeof obj, { str: 'world' }>>;
+        return obj.str;
+      })
+      .with(P.object, (obj) => {
+        type t = Expect<Equal<typeof obj, {
+          readonly str: string;
+        }>>;
+        return 'not found';
+      })
+      .exhaustive();
+    expect(res).toEqual('not found');
+  });
+
+  it('should match object with nested objects', () => {
+    const res = match({ x: { y: 1 } })
+      .with({ x: { y: 1 } }, (obj) => {
+        type t = Expect<Equal<typeof obj, { readonly x: { readonly y: 1 } }>>;
+        return 'yes';
+      })
+      .with(P.object, (obj) => {
+        type t = Expect<Equal<typeof obj, never>>;
+        return 'no';
+      })
+      .exhaustive();
+    expect(res).toEqual('yes');
+  });
+
+  it('should match object with nested objects and arrays', () => {
+    const res = match({ x: { y: [1] } })
+      .with({ x: { y: [1] } }, (obj) => {
+        type t = Expect<Equal<typeof obj, { x: { y: [1] } }>>;
+        return 'yes';
+      })
+      .with(P.object, (obj) => {
+        type t = Expect<Equal<typeof obj, { readonly x: { readonly y: readonly [1]}}>>;
+        return 'no';
+      })
+      .exhaustive();
+    expect(res).toEqual('yes');
+  });
+
+  it('should match empty object', () => {
+    const res = match({})
+      .with(P.object.empty(), (obj) => {
+        type t = Expect<Equal<typeof obj, {}>>;
+
+        return 'yes';
+      })
+      .with(P.object, (obj) => {
+        type t = Expect<Equal<typeof obj, never>>;
+
+        return 'no';
+      })
+      .exhaustive();
+    expect(res).toEqual('yes');
+  });
+
+  it('should match object with optional properties', () => {
+    const res = match({ x: 1 })
+      .with(P.object.empty(), (obj) => {
+        type t = Expect<Equal<typeof obj, { readonly x: 1; }>>;
+        return 'no';
+      })
+      .with(P.object, (obj) => {
+        type t = Expect<Equal<typeof obj, never>>;
+        return 'yes';
+      })
+      .exhaustive();
+    expect(res).toEqual('yes');
+  });
+});