强制执行可选类型打字稿

Question

Is there a way to enforce that a function can only get called with an optional type

where Optional is defined as

type Optional<T> = T | undefined

I would like to define a function f so that

declare type Foo = { foo: string }
declare var x: Optional<Foo>
declare var y: Foo

f(x) // ts typecheck ok
f(y) // ts typecheck ko 

Answer 1

As far as I can tell this works:

declare function f<T>(v:Optional<T> extends T ? T : never) : any;

Playground here