Type Alias OptionalIfVoid<T>

OptionalIfVoid: [T] extends [undefined | void] ? [t?: T] : [T]

Converts a type into a tuple whose element is optional when T is assignable to void | undefined.

Designed for rest parameters. The check considers the whole type, so a union such as string | undefined still requires an argument.

Type Parameters

T
The type to evaluate for optionality.

Example

function dispatch<T>(action: string, ...payload: OptionalIfVoid<T>): void {
    // ...
}

dispatch<void>("reset");          // Payload omitted
dispatch<number>("increment", 5); // Payload required
dispatch<number>("increment");    // Error: missing argument