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type IsAny<T> = 0 extends (1 & T) ? true : false; // https://stackoverflow.com/a/49928360/3406963
type IsNever<T> = [T] extends [never] ? true : false;
type IsUnknown<T> = IsNever<T> extends false ? T extends unknown ? unknown extends T ? IsAny<T> extends false ? true : false : false : false : false;
/**
Create a function type with a return type of your choice and the same parameters as the given function type.
Use-case: You want to define a wrapped function that returns something different while receiving the same parameters. For example, you might want to wrap a function that can throw an error into one that will return `undefined` instead.
@example
```
import type {SetReturnType} from 'type-fest';
type MyFunctionThatCanThrow = (foo: SomeType, bar: unknown) => SomeOtherType;
type MyWrappedFunction = SetReturnType<MyFunctionThatCanThrow, SomeOtherType | undefined>;
//=> type MyWrappedFunction = (foo: SomeType, bar: unknown) => SomeOtherType | undefined;
```
@category Function
*/
export type SetReturnType<Fn extends (...args: any[]) => any, TypeToReturn> =
// Just using `Parameters<Fn>` isn't ideal because it doesn't handle the `this` fake parameter.
Fn extends (this: infer ThisArg, ...args: infer Arguments) => any ? (
// If a function did not specify the `this` fake parameter, it will be inferred to `unknown`.
// We want to detect this situation just to display a friendlier type upon hovering on an IntelliSense-powered IDE.
IsUnknown<ThisArg> extends true ? (...args: Arguments) => TypeToReturn : (this: ThisArg, ...args: Arguments) => TypeToReturn
) : (
// This part should be unreachable, but we make it meaningful just in case…
(...args: Parameters<Fn>) => TypeToReturn
);
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33 entries across 33 versions & 1 rubygems