problems about name for namespace and template parameters

Question

Recently I read some code about websocketpp, and the following code is what I'm confused about:

#include <somefile.hpp>
template <typename config>
class endpoint : public config::socket_type {          //--------A--------//
    typedef typename config::concurrency_type concurrency_type;//-----B------//
    ....
}

In the somefile.hpp, there is namespace which also called config. So I don't know whether the name "config" in A and B denoted the that namespace or the template parameter. I guess it is template parameter.

Thx for all people asking my questions.

Answer 1

The name of the template parameter is introduced in the scope of the primary template declaration. It hides the name of the namespace.

From the C++ 17 Standard (6.3.2 Point of declaration)

11 The point of declaration for a template parameter is immediately after its complete template-parameter

With a requires clause the template declaration could look more clear.

Here is a demonstrative program

namespace config
{
}

template <typename config> requires requires { typename config::socket_type; }
class endpoint : public config::socket_type
{
};

struct A
{
    struct socket_type {};
};

int main()
{
    endpoint<A> e;
}