type-fest/source/is-symbol-literal.d.ts

A collection of essential TypeScript types

import type {CollapseLiterals, UnwrapBrand} from './internal/object.d.ts';
import type {IfNotAnyOrNever} from './internal/type.d.ts';

/**
Returns a boolean for whether the given type is a `symbol` [literal type](https://www.typescriptlang.org/docs/handbook/2/everyday-types.html#literal-types).

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

declare const symbolLiteral1: unique symbol;
declare const symbolLiteral2: unique symbol;

type A = IsSymbolLiteral<typeof symbolLiteral1>;
//=> true

type B = IsSymbolLiteral<symbol>;
//=> false

type C = IsSymbolLiteral<typeof symbolLiteral1 | typeof symbolLiteral2>;
//=> true
```

@category Type Guard
@category Utilities
*/
export type IsSymbolLiteral<T> = IfNotAnyOrNever<T, {
	ifNot: _IsSymbolLiteral<CollapseLiterals<UnwrapBrand<T>>>;
	ifAny: false;
	ifNever: false;
}>;

type _IsSymbolLiteral<T> = T extends symbol
	? symbol extends T
		? false
		: true
	: false;

export {};