gistfile1.txt

class MyClass
{
    function __construct(Collaborator %collaborator)
    {
    }
}

// vs.

class MyClass
{
    function doSomething(Collaborator $collaborator)
    {
    }
}

MyClass is composed by SomeHttpAction, which creates an implementation of Collaborator depending on some input parameter. SomeHttpAction and MyClass are created at the startup, while Collaborator is created after analyzing the request: that's why I find it handy to inject it as a parameter; from the point of view of MyClass nothing really changes.