C++

参考

<functional>

function template
<functional>

std::ref

reference (1)
template <class T> reference_wrapper<T> ref (T& elem) noexcept;
复制 (2)
template <class T> reference_wrapper<T> ref (reference_wrapper<T>& x) noexcept;
移动 (3)
 template <class T> void ref (const T&&) = delete;
Construct reference_wrapper
Constructs an object of the appropriate reference_wrapper type to hold a reference to elem.

If the argument is itself a reference_wrapper (2), it creates a copy of x instead.

The function calls the proper reference_wrapper constructor.

参数

elem
An lvalue reference, whose reference is stored in the object.
x
A reference_wrapper object, which is copied.

返回值

A reference_wrapper object of the appropriate type to hold an element of type T.

示例

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
 
// ref example
#include <iostream>     // std::cout
#include <functional>   // std::ref

int main () {
  int foo (10);

  auto bar = std::ref(foo);

  ++bar;

  std::cout << foo << '\n';

  return 0;
}

输出
11


数据竞争

The initialization version (1) does not access elem, but the returned object can be used to access or modify it.
The copying version (2) accesses its argument (x), returning an object that which can be used to access or modify its referred element.

异常安全

无异常保证： 绝不抛出异常。

另见

reference_wrapper::reference_wrapper
构造引用包装器 (public member function)
reference_wrapper::operator()
访问元素（函数形式） (public member function)
cref
构造指向 const 的 reference_wrapper (函数模板)