How do I Write a Custom Deleter to Handle Forward Declared Types

问题

Some older versions of visual-studio required a complete definition of the type for default_deleter to be defined. (I know this was the case in Visual Studio 2012 but I'd give bonus points to anyone who could tell me which version remedied this.)

To work around this I can write a custom_deleter function like so:

template <typename T>
void custom_deleter(T* param) {
    delete param;
}

And declare a smart pointer on a forward declared type like so: unique_ptr<Foo, function<void(Foo*)>> pFoo, assigning this pointer where Foo was completely declared like so: pFoo = decltype(pFoo)(new Foo, function(custom_deleter<Foo>))

Now as suggested here, I'd like to make my custom_deleter into a functor like this:

struct MyDeleter {
    template <typename T>
    void operator ()(T* param) {
        delete param;
    }
};

Which should allow me to declare: unique_ptr<Foo, MyDeleter> and assign: pFoo = decltype(pFoo)(new Foo) However when I try to do this in visual-studio-2012 I get: