Add P.object, P.object.empty and P.object.exact()

[gvergnaud]

TODO

• add unit tests and doc for P.object.exact({...})
• Make sure P.object.exact({ prop: P.select() }) works, both for type inference and runtime.

P.object predicates

P.object is itself a pattern, but also a module containing predicates related to object types.

P.object

P.object matches any value assignable to the object TypeScript type. This includes all object literals, but also arrays and functions!

P.object does not match primitive types, like strings or numbers.

import { match, P } from 'ts-pattern';

const fn = (input: unknown) =>
  match(input)
    .with(P.object, () => '✅')
    .otherwise(() => '❌');

console.log(fn({})); // ✅
console.log(fn({ hello: 'world!' })); // ✅
console.log(fn([])); // ✅
console.log(fn(() => {})); // ✅

console.log(fn(1, true, 'hi')); // ❌ ❌ ❌

P.object.empty()

P.object.empty() matches the empty object {}:

import { isMatching, P } from 'ts-pattern';

console.log(isMatching(P.object.empty(), {})); // true

P.object.empty() does not match empty arrays, 0 values or nullish values:

import { isMatching, P } from 'ts-pattern';

console.log(isMatching(P.object.empty(), [])); // false
console.log(isMatching(P.object.empty(), 0)); // false
console.log(isMatching(P.object.empty(), null)); // false
console.log(isMatching(P.object.empty(), undefined)); // false