How to forward declare an aliased template in c++

Question

I have the following aliased template:

#include <vector>

template <typename T>
using MyVector = std::vector <T>;

How can i forward declare MyVector?

template <typename T>
class MyVector;

does not work for me.

@HalilİbrahimOymacı [That makes no difference](http://stackoverflow.com/questions/2023977/c-difference-of-keywords-typename-and-class-in-templates). — mindriot, Jun 28 '16 at 06:45
Possible duplicate of [forward declare a template alias](http://stackoverflow.com/questions/16304468/forward-declare-a-template-alias) — PcAF, Jun 28 '16 at 08:07

score 2 · Answer 1 · answered Jul 17 '16 at 11:51

2

You might be able to get away with making it a type, which you will be able to forward-declare:

template <typename T>
struct MyVector: std::vector<T> {};

answered Jul 17 '16 at 11:51

AlwaysLearning

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score 1 · Accepted Answer · answered Jul 03 '16 at 15:11

You cannot forward declare an using declaration.
Anyway, you can declare forward a sort of traits as it follows:

#include <type_traits>
#include <vector>

template<typename>
struct MyStuff;

template<typename T>
auto f() { return typename MyStuff<T>::MyVector{}; }

template<typename T>
struct MyStuff {
    using MyVector = std::vector<T>;
};

int main() {
    static_assert(std::is_same<decltype(f<int>()), std::vector<int>>::value, "!");
}

How to forward declare an aliased template in c++

2 Answers2