type-fest/source/or.d.ts

A collection of essential TypeScript types

import type {If} from './if.d.ts';
import type {IsNever} from './is-never.d.ts';

/**
Returns a boolean for whether either of two given types are true.

Use-case: Constructing complex conditional types where multiple conditions must be satisfied.

@example
```
import type {Or} from 'type-fest';

type TT = Or<true, false>;
//=> true

type TF = Or<true, false>;
//=> true

type FT = Or<false, true>;
//=> true

type FF = Or<false, false>;
//=> false
```

Note: When `boolean` is passed as an argument, it is distributed into separate cases, and the final result is a union of those cases.
For example, `And<false, boolean>` expands to `And<false, true> | And<false, false>`, which simplifies to `true | false` (i.e., `boolean`).
@example
```
import type {And} from 'type-fest';

type A = Or<false, boolean>;
//=> boolean

type B = Or<boolean, false>;
//=> boolean

type C = Or<true, boolean>;
//=> true

type D = Or<boolean, true>;
//=> true

type E = Or<boolean, boolean>;
//=> boolean
```

Note: If `never` is passed as an argument, it is treated as `false` and the result is computed accordingly.

@example
```
import type {Or} from 'type-fest';

type A = Or<true, never>;
//=> true

type B = Or<never, true>;
//=> true

type C = Or<false, never>;
//=> false

type D = Or<never, false>;
//=> false

type E = Or<boolean, never>;
//=> boolean

type F = Or<never, boolean>;
//=> boolean

type G = Or<never, never>;
//=> false
```

@see {@link And}
*/
export type Or<A extends boolean, B extends boolean> =
	_Or<If<IsNever<A>, false, A>, If<IsNever<B>, false, B>>; // `never` is treated as `false`

export type _Or<A extends boolean, B extends boolean> = A extends true
	? true
	: B extends true
		? true
		: false;