CODEWITHSUNDEEP
c++templates
Omer Rosler
Omer Rosler

Reputation: 247

Template template parameter partial specialization c++

Consider the code:

template<template<typename,typename> class Container>
class A {
    template<class U, class Allocator>
    void Foo(Container<U, Allocator>*, U);
};

Now I want to specialize A in the case the Container is a map where the Value and Comparator are known, and create a definition of Foo in this case (no specialization of Foo). I tried this:

template<typename V, typename Comp> template<class U, class Allocator>
void A<std::map<typename, V, Comp, typename>>::Foo(map<U, V, Comp, Allocator>*, U ) {...}

But I get the compiling error:C3200: 'std::map<int,V,Comp,int>' : invalid template argument for template parameter 'Container', expected a class parameter.

I have looked online and only found similar issues, but I couldn't find a way to specify only partial template parameter list of a template template. Is there a way to do it?

EDIT: The only problem is when giving a template class partial specialization is to make it behave as a template with the remaining parameters. Here it's an attempt to think of a map<*,Known1,Known2,*> as a template of only 2 arguments (which can realy be used as the template template parameter of A) .

EDIT 2: The compiler I have to use is GCC 4.1.2 that has no support for template aliasing, which, as I understood, is a solution.

Upvotes: 4

Views: 3023

Answers (1)

Barry
Barry

Reputation: 303870

The problem is that A takes a template template parameter that takes two types:

template<template<typename,typename> Container>
class A {

But std::map doesn't take two types. It takes four:

template<
    class Key,
    class T,
    class Compare = std::less<Key>,
    class Allocator = std::allocator<std::pair<const Key, T> >
> class map;

So that's one problem. You will have to generalize your template to the following (also note the missing class keyword):

template <template <typename...> class Container>
class A { ... };

But even with that, at most you could completely explicitly specialize a member function, you can't partially specialize it:

template <>
template <>
void A<std::map>::Foo<>(std::map<U, V>*, U) { ... }

Upvotes: 5

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