C ++ decltype无法推断类型 [英] C++ decltype fails to deduce type

问题描述

在Visual Studio 2012中，decltype确实是个问题吗？还是应该很难使用？

Is decltype really buggy in Visual Studio 2012 or is it actually supposed to be this hard to use?

示例：

namespace ptl
{

    struct Test
    {
        Test(float ){}
    };

    template<class T, class A0>
    static T* static_constructor(void* p, A0 a0){return new(p) T(a0);}

    template<class T>
    T*  MakeVS2012Happy(T*);
}

inline auto ExampleFxn() -> decltype(ptl::MakeVS2012Happy(&ptl::static_constructor<ptl::Test, float>)) 
{
   return &ptl::static_constructor<ptl::Test, float>;
}
inline auto ExampleFxn2() -> decltype(&ptl::static_constructor<ptl::Test, float>)
{
   return &ptl::static_constructor<ptl::Test, float>;
}

ExampleFxn会进行编译，因为我已使用无意义的函数将代码包装在decltype中

ExampleFxn compiles because I've wrapped the code in the decltype with that pointless function.

ExampleFxn2没有，VS2012发出非常有用的错误消息：

ExampleFxn2 does not, VS2012 spits out the extremely helpful error message:

错误C3555：错误的参数'decltype'

error C3555: incorrect argument to 'decltype'

有人知道是什么原因吗？我似乎经常需要与decltype对抗，以使其按预期工作……

Anyone know what causes this? I seem to constantly have to fight against decltype to get it to work as expected...

谢谢

推荐答案

& ptl :: static_constructor< ptl :: Test，float> 的类型可以由推导decltype（）。这看起来像MSVC ++中的错误。 clang和gcc都认为代码很好（假设添加了 #include< new> ）。

The type of &ptl::static_constructor<ptl::Test, float> can be deduced by decltype(). This looks like a bug in MSVC++. Both clang and gcc agree that the code is fine (assuming #include <new> is added).

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