Just like in case of the function arguments, template parameters can have their default values. All template parameters with a default value have to be declared at the end of the template parameter list.
A template argument for a template template parameter is the name of a class template. When the compiler tries to find a template to match the template template argument, it only considers primary class templates. (A primary template is the template that is being specialized.)
Can default arguments be used with the template class? Explanation: The template class can use default arguments.
Why we use :: template-template parameter? Explanation: It is used to adapt a policy into binary ones.
I'd like to ask whether the following code sample should compile:
#include <iostream>
#include <vector>
#include <typeinfo>
using namespace std;
template <template <class...> class C>
struct convert_container
{
using type = C<double>;
// Visual Studio requires this to be:
// using type = C<double, std::allocator<doble>>
};
int main()
{
std::cout << typeid(convert_container<std::vector>::type).name();
}
The code compiles fine with GCC 4.8.1 and Clang 3.4 but not with Visual Studio 2013. The error I get:
error C2976: 'std::vector' : too few template arguments
c:\program files (x86)\microsoft visual studio 12.0\vc\include\vector(650) : see declaration of 'std::vector'
c:\users\michał\documents\visual studio 2013\projects\transform\transform.cpp(14) : see reference to class template instantiation 'convert_container<std::vector>' being compiled
What does the standard say about this? Am I required to explicitly state all the parameters (including defaulted ones) when using the template template parameter C
or is this just a bug in VC++?
Context: The issue araised from Constructor's answer to my previous question: https://stackoverflow.com/a/23874768/2617356
When searching the archives I've found this question: Default values in templates with template arguments ( C++ ) It's basically about the same problem, the question author states that default parameters for template template parameter "had to be" explicitly stated. However, the asker accepted solution that's not quite applicable in my case. The question was not about what is the standard-conforming behaviour, so I believe this is not a duplicate.
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