CODEWITHSUNDEEP
c++c++11
Steve Lorimer
Steve Lorimer

Reputation: 28659

template 'using' declaration not working

I have the following little test application, where I'm trying to employ a template using declaration.

However, it doesn't compile. (I'm using gcc 4.6.1)

src/main.cpp:36:3: error: expected unqualified-id before ‘using’

Any insight greatly appreciated!

#include <iostream>
#include <utility>

template<typename F, typename... Args>
struct invoke;

// specialisation of invoke for 1 parameter
template<typename F, typename A0>
struct invoke<F, A0>
{
  invoke(F& f_, A0&& a0_)   
    : _f(f_)
    , _a0(std::move(a0_))
  {} 

  void operator()()
  {
    _f(_a0);
  } 

  F _f;
  A0 _a0;
};

template<typename F>
struct traits;

// fwd declaration for handler
struct handler;

// specialisation of traits for handler
template<>
struct traits<handler>
{
  template<class F, typename... Args>
  using call_t = invoke<F, Args...>;               // line 36
};

template<typename F>
struct do_it
{
  template<typename... Args>
  void operator()(F& _f, Args... args)
  {
    // create an object of the type declared in traits, and call it
    typename traits<F>::template call_t<F, Args...> func(_f, std::forward<Args>(args)...);
    func();
  }
};

struct handler
{
  void operator()(int i)
  {
    std::cout << i << std::endl; 
  }
};

int main()
{
  handler h;

  do_it<handler> d;
  d(h, 4);

  return 0;
}

Upvotes: 2

Views: 2326

Answers (1)

Pubby
Pubby

Reputation: 53047

According to this: http://wiki.apache.org/stdcxx/C++0xCompilerSupport and this: http://gcc.gnu.org/projects/cxx0x.html

Template aliases aren't in GCC 4.6\ There should be a patch which fixes it.

(I may be mistaken that you're using template aliases and so this might not apply to you. I'm not very familiar with C++11)

Upvotes: 3

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