Getting typename from collection.

I'm curious how exactly Unity has implemented the GetComponent function.

Assuming some sort of collection is storing the components -

 public T GetComponent<T>() where T : Component
 {
     ????
 }

How do we find a component of type T inside of the collection? Another question is how would you enforce unique components based on Type? For example the component collection couldn't store two FooComponent : Component types.

I'm aware that we can get typeof(T) and compare that type to each in the collection to find a match but I'm curious if there's a better way to do so.