IsNever<T>
IsNever<
T
> = [T
] extends [never
] ?true
:false
Defined in: packages/react-querybuilder/src/types/type-fest/is-never.ts:41
Returns a boolean for whether the given type is never
.
Type Parameters
Type Parameter |
---|
T |
Link
https://github.com/microsoft/TypeScript/issues/31751#issuecomment-498526919
Link
https://stackoverflow.com/a/53984913/10292952
Link
https://www.zhenghao.io/posts/ts-never
Useful in type utilities, such as checking if something does not occur.
Example
import type {IsNever, And} from 'type-fest';
// https://github.com/andnp/SimplyTyped/blob/master/src/types/strings.ts
type AreStringsEqual<A extends string, B extends string> =
And<
IsNever<Exclude<A, B>> extends true ? true : false,
IsNever<Exclude<B, A>> extends true ? true : false
>;
type EndIfEqual<I extends string, O extends string> =
AreStringsEqual<I, O> extends true
? never
: void;
function endIfEqual<I extends string, O extends string>(input: I, output: O): EndIfEqual<I, O> {
if (input === output) {
process.exit(0);
}
}
endIfEqual('abc', 'abc');
//=> never
endIfEqual('abc', '123');
//=> void
caution
API documentation is generated from the latest commit on the main
branch. It may be somewhat inconsistent with official releases of React Query Builder.