c++ - g++ 4.7.2 用于类型别名的处理似乎被打破

Question

在下面的代码中，g++ 4.7.2 会被基于using 的类型别名混淆。

代码:

#include <map>

enum class Direction
{
  UP=-1,
  DOWN=1
};

template <Direction dir>
struct Comparator
{
  bool operator()(int lhs, int rhs) const
  {
    return lhs<rhs; // Comparison should be based on dir
                    // but let's not even use dir for now
  }
};

template <Direction dir>
using IntToIntMap=std::map<int, int, Comparator<dir>>;

template <Direction dir>
void TestFunc()
{
  using TheMap=IntToIntMap<dir>; // TheMap should be a synonym for
                                 // IntToIntMap<dir>

  typename IntToIntMap<dir>::value_type value1; // This compiles
  typename TheMap::value_type value2;           // This does not (???)
}

int main()
{
  TestFunc<Direction::UP>();
}

编译代码:

g++ -std=c++11 -Wall --pedantic -o test test.cpp

意外的编译时错误:

test.cpp: In instantiation of 'void TestFunc() [with Direction dir = 
                                                (Direction)-1]
test.cpp:34:29:   required from here
test.cpp:29:33: error: no type named 'value_type' in 'using TheMap = 
                                      IntToIntMap<dir>'

有问题的行有什么问题？代码是否违反了 C++11 标准，或者这是一个 g++ 4.7.2 错误？ Live code in g++-4.7

Answer 1

根据评论，它已在 gcc-4.8 中修复:

4.7:http://coliru.stacked-crooked.com/view?id=9d55db125baaac0b169e61bbcfcb2a26-f2a3752efd0426bdaa29babef505f76e

4.8:http://coliru.stacked-crooked.com/a/6cd0ad895d067e51