具有多个参数的绑定函数导致C2027 [英] Binding functions with multiple arguments results in C2027

问题描述

我使用ChaiScript 5.3.1，我试图绑定函数到我自己的类，特别是setPosition函数，可以采取Vector3或3个浮动。

类和它的相关方法声明如下：

 类DLLExport Actor 
 {
 public：
 Actor（Level * level，const String& name，Actor * parent）; 
 virtual〜Actor（）; 
 
 void setPosition（const Real& x，const Real& y，const Real& z）; 
 void setPosition（const Vector3& position）; 
}; 
  

，我试着像这样绑定：

  m-> add（user_type< Actor>（），Actor）; 
 m-> add（fun< void（Actor :: *）（const Vector3&）>（& Actor :: setPosition），setPosition）; 
  

这将产生以下编译器输出（Windows，MSVC 2013）：

  2功能（550）：错误C2027：使用未定义类型'std :: _ Get_function_impl< _Fty>'
 2> with 
 2> [
 2> _Fty = void（__thiscall Actor :: *）（const Vector3&）
 2> ] 
 2> .. \..\ScriptingDemo\Binder.cpp（60）：参见类模板实例化'std :: function< void（__thiscall Actor :: *）（const Vector3&）& b $ b 2功能（551）：错误C2504：'type'：基类未定义
 2功能（554）：错误C2027：使用未定义类型'std :: _ Get_function_impl <_Fty>'
 2& with 
 2> [
 2> _Fty = void（__thiscall Actor :: *）（const Vector3&）
 2> ] 
 2功能（554）：错误C2146：语法错误：缺少';'标识符'_Mybase'
 2功能（554）：错误C4430：缺少类型说明符注意：C ++不支持default-int 
  

解决方案

编译器错误。 Clang和GCC都接受此SSCCE ，Visual C ++不接受。

这四个重载函数 chaiscript :: fun 声明如下：

  / * 1 * / template< typename T> 
 Proxy_Function fun（T t）; 
 
 / * 2 * / template< typename T> 
 Proxy_Function fun（const std :: function< T>& f）; 
 
 / * 3 * / template< typename T，typename Q> 
 Proxy_Function fun（T t，const Q& q）; 
 
 / * 4 * / template< typename T，typename Q，typename R> 
 Proxy_Function fun（T t，const Q& q，const R& r）; 
  

根据语言规则，此表达式：

  fun< void（Actor :: *）（const Vector3&）>（& Actor :: setPosition）
  

结果调用重载1或重载2，重载解析将决定哪个。

显式模板参数，这是重载解决方案必须使用：

  / * 1 * / Proxy_Function fun Actor :: *）（const Vector3&）t）; 
 / * 2 * / Proxy_Function fun（const std :: function< void（Actor :: *）（const Vector3&）>& f）; 
  

std :: function< void（Actor :: *）（const Vector3&）> 是一个未定义的类型，所以重载2是不可行的。 Visual C ++似乎认为这是一个错误，但它不应该。

使用您的解决方法：

  fun（（void（Actor :: *）（const Vector3&））& Actor :: setPosition）
   
 
您正在将类型重载的成员函数& Actor :: setPosition 的指针转换为类型 void Actor :: *）（const Vector3&）并允许模板参数推导进入，Visual C ++满足。
 
 
 
将更好地避免C风格的转换：
  fun（static_cast< void（Actor :: *）（const Vector3& ）>（& Actor :: setPosition））
  
 
I'm using ChaiScript 5.3.1, and I'm trying to bind functions to my own class, specifically a setPosition function which can take either a Vector3 or 3 floats.

The class and it's relevant methods are declared like so:
class DLLExport Actor
{
public:
        Actor(Level* level, const String& name, Actor* parent);
        virtual ~Actor();

        void setPosition(const Real& x, const Real& y, const Real& z);
        void setPosition(const Vector3& position);
};
and I'm trying to bind them like this:
m->add(user_type<Actor>(), "Actor");
m->add(fun<void (Actor::*)(const Vector3&)>(&Actor::setPosition), "setPosition");
This results in the following compiler output (Windows, MSVC 2013):
 2functional(550): error C2027: use of undefined type 'std::_Get_function_impl<_Fty>'
 2>          with
 2>          [
 2>              _Fty=void (__thiscall Actor::* )(const Vector3 &)
 2>          ]
 2>          ..\..\ScriptingDemo\Binder.cpp(60) : see reference to class template instantiation 'std::function<void (__thiscall Actor::* )(const Vector3 &)>' being compiled
 2functional(551): error C2504: 'type' : base class undefined
 2functional(554): error C2027: use of undefined type 'std::_Get_function_impl<_Fty>'
 2>          with
 2>          [
 2>              _Fty=void (__thiscall Actor::* )(const Vector3 &)
 2>          ]
 2functional(554): error C2146: syntax error : missing ';' before identifier '_Mybase'
 2functional(554): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int

解决方案
This is a compiler bug. Clang and GCC both accept this SSCCE, Visual C++ does not.

The four overloaded functions chaiscript::fun are declared as so:
/*1*/ template <typename T>
      Proxy_Function fun (T t);

/*2*/ template <typename T>
      Proxy_Function fun (const std::function< T > &f);

/*3*/ template <typename T, typename Q>
      Proxy_Function fun (T t, const Q &q);

/*4*/ template <typename T, typename Q, typename R>
      Proxy_Function fun (T t, const Q &q, const R &r);
According to the language rules, this expression:
fun<void (Actor::*)(const Vector3&)>(&Actor::setPosition)
Results in a call to either overload 1 or overload 2, overload resolution will determine which.

After substituting the explicit template argument, this is what overload resolution will have to work with:
/*1*/ Proxy_Function fun (void (Actor::*)(const Vector3&) t);
/*2*/ Proxy_Function fun (const std::function< void (Actor::*)(const Vector3&) > &f);
std::function< void (Actor::*)(const Vector3&) > is an undefined type, so overload 2 is not viable. Visual C++ seems to think that this constitutes an error, but it should not.

With your workaround:
fun((void(Actor::*)(const Vector3&))&Actor::setPosition)
You are casting the pointer to overloaded member function &Actor::setPosition to the type void(Actor::*)(const Vector3&) and allowing template argument deduction to step in, and Visual C++ is content with that.

You would be even better off avoiding C-style casts:
fun(static_cast<void(Actor::*)(const Vector3&)>( &Actor::setPosition ))


                        
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