在C ++中将临时变量作为非const引用 [英] Passing temporaries as non-const references in C++

问题描述

我有以下代码片段，例如dec_proxy尝试反转增量运算符对复杂函数调用foo中执行的类型的影响 - 其中btw不能更改接口。

I have the following piece of code, as an example dec_proxy attempts to reverse the effects of the increment operator upon the type that is executed in a complex function call foo - which btw I cannot change the interface of.

#include <iostream>

template<typename T>
class dec_proxy
{
public:
   dec_proxy(T& t)
   :t_(t)
   {}

   dec_proxy<T>& operator++()
   {
      --t_;
      return *this;
   }

private:
   T& t_;
};

template<typename T, typename S, typename R>
void foo(T& t, S& s, R& r)
{
  ++t;
  ++s;
  ++r;
}

int main()
{
   int i = 0;
   double j = 0;
   short  k = 0;

   dec_proxy<int> dp1(i);
   dec_proxy<double> dp2(j);
   dec_proxy<short> dp3(k);

   foo(dp1,dp2,dp3);

   //foo(dec_proxy<int>(i),     <---- Gives an error
   //   dec_proxy<double>(j),     <---- Gives an error
   //   dec_proxy<short>(k));      <---- Gives an error 

   std::cout << "i=" << i << std::endl;

   return 0;
}

问题是对于各种类型我想使用dec_proxy I目前需要创建一个专门的dec_proxy实例 - 它似乎是一个非常混乱和有限的方法。

The problem is that for the various types I'd like to use dec_proxy I currently require creating a specialized instance of dec_proxy - it seems like a very messy and limited approach.

我的问题是：将这种短暂临时变量作为非const引用参数传递的正确方法是什么？

My question is: What is the correct way to pass such short-lived temporaries as non-const reference parameters?

推荐答案

采取斯蒂芬的建议，你应该看看如何使非const引用不能绑定到临时对象？，只需添加一个成员函数，返回一个引用 dec_proxy ，例如：

Taking Stephen's advice, you should look at the answer to How come a non-const reference cannot bind to a temporary object? and simply add a member function that returns a reference dec_proxy, e.g.:

dec_proxy& ref（）{return * this; }

并致电 foo ：

foo(
    dec_proxy<int>(i).ref(), 
    dec_proxy<double>(j).ref(), 
    dec_proxy<short>(k).ref());

我很肯定编译。

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