为什么 Visual Studio 2013 遇到此类成员 decltype 的问题?

#include <vector>

struct C
{
    std::vector<int> v;
    decltype(v.begin()) begin() { return v.begin(); }
    decltype(v.end()) end() { return v.end(); }
};

Clang++没有问题,但是MSVC 2013报错如下:

Clang++ has no problem, but MSVC 2013 gives the following error:

error C2228: left of '.begin' must have class/struct/union

推荐答案

这是 VS2013 中的已知错误,已修复 在 VS2015 中.如果您改用尾随返回类型,编译器将接受该代码.

This is a known bug in VS2013, fixed in VS2015. The compiler will accept the code if you use a trailing return type instead.

struct C
{
    std::vector<int> v;
    auto begin() -> decltype(v.begin()) { return v.begin(); }
    auto end()   -> decltype(v.end())   { return v.end(); }
};

正如错误报告所说,另一种解决方法是使用:

As the bug report says, another work around is by using:

struct C
{
    std::vector<int> v;
    decltype(std::declval<decltype(v)>().begin()) begin() { return v.begin(); }
    decltype(std::declval<decltype(v)>().end())   end()   { return v.end(); }
};

但正如@BenVoigt 在评论中指出的那样,阅读这个答案 了解为什么尾随返回类型应该是首选选项.

But as @BenVoigt points out in the comments, read this answer for why the trailing return type should be the preferred option.

在链接页面中搜索未完全实现的类成员访问的C++ decltype

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