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c++templatesc++11using

using type = smth. and templated types

I have some trouble with a piece of C++ code.

First, if I do this, it works quite well :

struct A
{
    using my_type1 = double;
    using my_type2 = int;
};

struct B
{
    using size_type = A::my_type2;
};

However, I want to be able to choose my_type1, so I went the template way : 

template <typename T>
struct A
{
    using my_type1 = T;
    using my_type2 = int;
};

template <typename T>
struct B
{
    using size_type = A<T>::my_type2;
};

Here, gcc fails with : "expected type specifier" on the line 

using size_type = A<T>::my_type2;

I could just put my_type2 in template too but this is a type that shouldn't change much.

So why doesn't my method work ? Thanks!

Solution

  • You have to add typename:

    using size_type = typename A<T>::my_type2;