指向成员的指针：在GCC中工作，但不在VS2015中 [英] Pointer to member: works in GCC but not in VS2015

问题描述

我想实现一个属性系统来将C ++实例转换为JSON，反之亦然。我参考了Guillaume Racicot在这个问题中的回答（ C ++ JSON序列化）的一部分代码，简化了它。

这是我如何进行。我有一个属性类：

  template< typename Class，typename T> 
 struct Property {
 constexpr Property（T Class :: * member，const char * name）：m_member（member），m_name（name）{} 
 
 T类:: * m_member; 
 const char * m_name; 
}; 
  

m_member指向 Class

假设我想为 User 类定义属性，我希望能够像这样，以便能够为成员分配属性名称：

  class User 
 {
 public：
 int age; 
 
 constexpr static auto properties = std :: make_tuple（
 Property< User，int>（& User :: age，age）
）;这个代码在GCC（http://coliru.stacked-crooked.com/a/276ac099068579fd ），但不是在Visual Studio 2015更新3.我得到这些错误： / p> 
 
 
  main.cpp（19）：错误C2327：'User :: age'：不是类型名称，静态或枚举
 main.cpp（19）：error C2065：'age'：undeclared identifier 
 main.cpp（20）：error C2672：'std :: make_tuple'：找不到匹配的重载函数
 main.cpp（20）：error C2119：'properties'：'auto'的类型不能从空的初始化器中推导
  
 
 b $ b 
有没有解决方法，使其工作在Visual Studio 2015更新3？
解决方案
只是用属性成员函数替换属性成员数据：
  class User 
 {
 public：
 int age; 
 
 constexpr static auto properties（）{return std :: make_tuple（
 Property< User，int>（& User :: age，age）
）; } 
}; 
  
这是因为在成员函数的定义中，类被认为是完全定义的。它还具有期望的属性，如果使用odr，属性不需要单独定义。
 
I'm trying to implement a "property" system to convert C++ instances into JSON and vice versa. I took a part of the code from Guillaume Racicot's answer in this question (C++ JSON Serialization) and simplified it.

Here is how I proceed. I have a Property class:
template <typename Class, typename T>
struct Property {
    constexpr Property(T Class::* member, const char* name) : m_member(member), m_name(name) {}

    T Class::* m_member;
    const char* m_name;
};
m_member points to a specific member of Class

Let's say I want to define properties for a User class, I would like to be able to proceed like this, to be able to assign members a property name:
class User
{
public:
    int age;

    constexpr static auto properties = std::make_tuple(
        Property<User, int>(&User::age, "age")
    );
}
This code compiles and works correctly in GCC(http://coliru.stacked-crooked.com/a/276ac099068579fd) but not in Visual Studio 2015 Update 3. I get those errors:
main.cpp(19) : error C2327 : 'User::age' : is not a type name, static, or enumerator
main.cpp(19) : error C2065 : 'age' : undeclared identifier
main.cpp(20) : error C2672 : 'std::make_tuple' : no matching overloaded function found
main.cpp(20) : error C2119 : 'properties' : the type for 'auto' cannot be deduced from an empty initializer
Would there be a workaround to make it work in Visual Studio 2015 Update 3?
解决方案
My preferred workaround is just to replace the properties member data with a properties member function:
class User
{
public:
    int age;

    constexpr static auto properties() { return std::make_tuple(
        Property<User, int>(&User::age, "age")
    ); }
};
This works because in the definition of a member function, the class is considered to be completely defined. It also has the desirable attribute that properties doesn't need to be separately defined if odr-used.

                        
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