https://github.com/buschtoens/combine-type-predicates

Combine user-defined type guards / type predicates as unions and intersections.
https://github.com/buschtoens/combine-type-predicates

intersection-types type-guard type-guards type-predicates typescript union-types

Last synced: 2 months ago
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Combine user-defined type guards / type predicates as unions and intersections.

• Host: GitHub
• URL: https://github.com/buschtoens/combine-type-predicates
• Owner: buschtoens
• License: isc
• Created: 2020-04-01T17:06:26.000Z (over 4 years ago)
• Default Branch: master
• Last Pushed: 2023-12-15T14:48:37.000Z (about 1 year ago)
• Last Synced: 2024-10-09T12:42:36.974Z (2 months ago)
• Topics: intersection-types, type-guard, type-guards, type-predicates, typescript, union-types
• Language: TypeScript
• Size: 83 KB
• Stars: 7
• Watchers: 3
• Forks: 1
• Open Issues: 12
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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README

        
# combine-type-predicates

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Combine [user-defined type guards / type predicates][user-defined-type-guards]

as [unions][union] and [intersections][intersection].

[user-defined-type-guards]: https://www.typescriptlang.org/docs/handbook/advanced-types.html#user-defined-type-guards

[union]: https://www.typescriptlang.org/docs/handbook/advanced-types.html#union-types

[intersection]: https://www.typescriptlang.org/docs/handbook/advanced-types.html#intersection-types

```ts

import { isSome, isEvery } from 'combine-type-predicates';

type Foo = { foo: boolean; baz: number };

type Bar = { bar: symbol; baz: string };

const isFoo = (v: unknown): v is Foo

  => typeof v.foo === 'boolean' && typeof v.baz === 'number';

const isBar = (v: unknown): v is Bar

  => typeof v.bar === 'symbol' && typeof v.baz === 'string';

const isFooOrBar = isSome(isFoo, isBar);

// => (subject: unknown) => subject is Foo | Bar

const isFooAndBar = isEvery(isFoo, isBar);

// => (subject: unknown) => subject is Foo & Bar

const x: unknown = undefined;

if (isFooOrBar(x)) {

  x.baz; // => string | number

  if ('foo' in x) {

    x.foo; // => boolean

  } else {

    x.bar; // => symbol

  }

}

if (isFooAndBar(x)) {

  x.foo; // => boolean

  x.bar; // => symbol

  x.baz; // => never (no such thing as `string & number`)

}

```