TS2345 Argument of type A is not assignable to parameter of type A

[CarsonF]

TypeScript Version:

1.8.0

Code

declare function decorate<T>(): (component: T) => T;

class Foo {
  derp () {}
}

decorate<Foo>()(Foo);

error TS2345: Argument of type 'typeof Foo' is not assignable to parameter of type 'Foo'.
  Property 'derp' is missing in type 'typeof Foo'.

How can there be a type mismatch if it's the same type? 😖

[yortus]

Your decorate<Foo>() call returns a function that accepts and returns an instance of Foo, but then you pass it the constructor function Foo, which is not the same type, hence the error.

I'm not sure whether you mean to work with Foo instances or Foo constructors, but the following variants both pass type checks:

decorate<typeof Foo>()(Foo);  // Foo constructor
decorate<Foo>()(new Foo);  // Foo instance

[CarsonF]

@yortus Ahh thank you, that's what I was missing.

Thank you @blakeembrey as well :)