为什么从C ++ 11中删除了unary_function，binary_function？ [英] Why have unary_function, binary_function been removed from C++11?

问题描述

我发现 binary_function 已从C ++ 11中删除。我想知道为什么。

I found that binary_function is removed from C++11. I am wondering why.

C ++ 98：

template <class T> struct less : binary_function <T,T,bool> {
  bool operator() (const T& x, const T& y) const {return x<y;}
};

C ++ 11：

template <class T> struct less {
  bool operator() (const T& x, const T& y) const {return x<y;}
  typedef T first_argument_type;
  typedef T second_argument_type;
  typedef bool result_type;
};

已修改 ------------- -------------------------------------------------- -------------

MODIFIED----------------------------------------------------------------------------

template<class arg,class result>
struct unary_function
{
       typedef arg argument_type;
       typedef result result_type;
};

例如，如果我们要为功能编写适配器，甚至在C ++ 98中，

For example, if we want to write our adapter for function even in C++98,

template <class T> struct even : unary_function <T,bool> {
  bool operator() (const T& x) const {return 0==x%2;}
};

find_if(bgn,end,even<int>()); //find even number

//adapter
template<typename adaptableFunction >
class unary_negate
{
   private:
       adaptableFunction fun_;
   public:
       typedef adaptableFunction::argument_type argument_type;

       typedef adaptableFunction::result_type result_type;  
       unary_negate(const adaptableFunction &f):fun_(f){}

       bool operator()(const argument_type&x) 
       {
           return !fun(x);
       }
}

find_if(bgn,end, unary_negate< even<int> >(even<int>()) ); //find odd number

在没有 unary_function ？

推荐答案

它并未删除，只是在C ++ 11中已弃用。它仍然是C ++ 11标准的一部分。您仍然可以在自己的代码中使用它。

It isn't removed, it's just deprecated in C++11. It's still part of the C++11 standard. You can still use it in your own code. It was removed in C++17 though.

在标准中不再使用 ，因为要求实现从<$派生c $ c> binary_function 是超规格的。

It isn't used in the standard any more because requiring implementations to derive from binary_function is over-specification.

用户不必担心是否少从 binary_function 派生而来，他们只需要注意它定义了 first_argument_type ， second_argument_type 和 result_type 。

Users should not care whether less derives from binary_function, they only need to care that it defines first_argument_type, second_argument_type and result_type. It should be up to the implementation how it provides those typedefs.

强制实现从特定类型派生意味着用户可能开始依赖于该派生，这使得实现没有任何类型定义。感觉并且没有用。

Forcing the implementation to derive from a specific type means that users might start relying on that derivation, which makes no sense and is not useful.

编辑

在没有unary_function的情况下，如何在c ++ 11中改进它？

How can we improve this in c++11 without unary_function?

您不需要它。

template<typename adaptableFunction>
class unary_negate
{
   private:
       adaptableFunction fun_;
   public:
       unary_negate(const adaptableFunction& f):fun_(f){}

       template<typename T>
           auto operator()(const T& x)  -> decltype(!fun_(x))
           {
               return !fun_(x);
           }
}

事实上，您可以做得更好，请参见 not_fn ：广义否定符

In fact you can do even better, see not_fn: a generalized negator

这篇关于为什么从C ++ 11中删除了unary_function，binary_function？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！