访问单个类型的可变模板 [英] Accessing individual types of variadic templates

问题描述

我在C ++ 11中创建了一个lua绑定。我想在一个可变参数模板中处理每个类型。

我想我可以这样做，除了使用 Params ... 表示其中的所有类型，而不是其中的下一个单独类型，如可变参数函数参数。

  template< class T，typename ReturnType，typename ... Params> 
 struct MemberFunctionWrapper< ReturnType（T :: *）（Params ...）> 
 {
 
 static int CFunctionWrapper（lua_State * luaState）
 {
 for（int i = 0; i  {
 //我想获得下一个类型，而不是所有的类型
 CheckLuaValue< Params ...>（）; 
 //做其他事情
} 
} 
}; 
  

我该如何做？

 
您可以通过扩展函数调用后扩展到
  //把它放在你的命名空间中
 struct Lunch {template< typename ... T>午餐（T ...）{}}; 
 
 //而不是for循环
午餐{（CheckLuaValue< Params>（），void（），0）...} 
  

您可以使用lambda做其他事情。你甚至可以让你的 i 递增

  static int CFunctionWrapper（lua_State * luaState）
 {
 int i = 0; 
 Lunch {
（CheckLuaValue< Params>（），
 [&] {std :: cout<<param<< i< std :: endl;}（），
 ++ i）... 
}; 
} 
  

请注意，标准支持将所有内容放入lambda。编译器支持直到最近（上次我检查）不是很好，虽然

  static int CFunctionWrapper（lua_State * luaState）
 {
 int i = 0; 
 Lunch {（[&] {
 CheckLuaValue< Params>（）; 
 std :: cout<<<This is param<< i< std :: endl; 
}（），++ i）... 
}; 
} 
  




I am creating a lua binding in C++11. I want to process each type in a variadic template.

I was thinking I could do something like this, except using Params... represents all of the types inside of it, and not a the next single type inside of it like variadic function parameters do.

template <class T, typename ReturnType, typename... Params>
struct MemberFunctionWrapper <ReturnType (T::*) (Params...)>
{

    static int CFunctionWrapper (lua_State* luaState)
    {
        for(int i = 0; i < sizeof...(Params); i++)
        {
             //I want to get the next type, not all of the types
             CheckLuaValue<Params...>();
             //Do other stuff
        }
    }
};

How would I go about doing this?

解决方案

You can do this by simply expanding after the function call, into something that can be expanded to.

// put this in your namespace
struct Lunch { template<typename ...T> Lunch(T...) {} }; 

// and this instead of the for loop
Lunch{ (CheckLuaValue<Params>(), void(), 0)... };

You can do something else with a lambda. You can even have your i incremented

static int CFunctionWrapper (lua_State* luaState)
{
    int i = 0;
    Lunch{ 
      (CheckLuaValue<Params>(), 
       [&]{ std::cout << "That was param " << i << std::endl; }(),
       ++i)... 
    };
}

Note that the Standard supports putting everything into the lambda. Compiler support until recently (last time I checked) wasn't very good though

static int CFunctionWrapper (lua_State* luaState)
{
    int i = 0;
    Lunch{([&]{ 
       CheckLuaValue<Params>();
       std::cout << "That was param " << i << std::endl;
    }(), ++i)... 
    };
}

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