VS2015 C ++：无法将函数定义与现有声明匹配 [英] VS2015 C++ : unable to match function definition to an existing declaration

问题描述

我试图使NCORR库在VS2015 C ++上工作。

I try to make NCORR library work on VS2015 C++. The library was originally written on Linux.

作为库的一部分，有类似于

As part of the library there is code similar to

#include <chrono>

template<typename T_container>
struct container_traits {
    typedef typename T_container::container              nonconst_container;
};


template <typename T_container>
class base_region {
public:

    typedef typename container_traits<T_container>::nonconst_container nonconst_container;

    template<typename T_container2>
    typename std::enable_if<std::is_same<typename container_traits<T_container2>::nonconst_container, typename nonconst_container>::value, base_region&>::type operator=(const base_region<T_container2>&);
};

template <typename T_container>
template <typename T_container2>
typename std::enable_if<std::is_same<typename container_traits<T_container2>::nonconst_container, typename base_region<T_container>::nonconst_container>::value, base_region<T_container>&>::type base_region<T_container>::operator=(const base_region<T_container2>& reg) {
    return *this;
}


int main()
{
    return 0;
}

当我尝试在VS2015 win32控制台应用程序上编译代码时， / p>

When I try to compile the code on VS2015 win32 console application, I get

C2244   'base_region<T_container>::operator =': unable to match function definition to an existing declaration  ConsoleApplication5

我认为问题是 typename nonconst_container $ c> typename base_region< T_container> :: nonconst_container 在定义中。

I think the problem is typename nonconst_container in declaration vs typename base_region<T_container>::nonconst_container in definition.

你知道什么是错的， ？

Do you know what is wrong and how can I make the code work?

推荐答案

首先， typename nonconst_container typename 只允许在限定名称之前。

First, typename nonconst_container is ill-formed. typename is only allowed before a qualified name.

MSVC似乎有匹配 nonconst_container在类模板定义中的和在类外成员函数定义中的 typename base_region< T_container> :: nonconst_container 。

MSVC seems to have problems matching nonconst_container in the class template definition and the typename base_region<T_container>::nonconst_container in the out-of-class member function definition.

解决方法（也较短）是使用 trailing-return-type ：

A workaround (which is also shorter) is to use a trailing-return-type:

template <typename T_container>
template <typename T_container2>
auto base_region<T_container>::operator=(const base_region<T_container2>& reg)
  -> typename std::enable_if<std::is_same<typename container_traits<T_container2>::nonconst_container,
                                          nonconst_container>::value, base_region&>::type 
                                       // ^^^^^^^^^^^^^^^^^^          ^^^^^^^^^^^
{
   //...
}

base_region< T_container> :: operator = 之后的所有内容在成员函数体中使用（特别是，它将首先查看类成员），所以你可以写 nonconst_container 和 base_region& ，并愉快地回避MSVC错误。

Everything after base_region<T_container>::operator= gets looked up just like a name used in the member function body (in particular, it will first look at class members), so you can just write nonconst_container and base_region&, and happily sidestep the MSVC bug.

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