std::reference_wrapper
STD：：参考资料[医]包装器
| Defined in header | | |
|---|---|---|
| template< class T > class reference_wrapper; | | (since C++11) |
std::reference_wrapper是一个类模板，它将引用包装在可复制的可分配对象中。它经常被用作在标准容器%28中存储引用的机制。std::vector%29通常不能保存引用。
特别是，std::reference_wrapper是CopyConstructible和CopyAssignable对对象的引用或对类型函数的引用的包装器T...的例子std::reference_wrapper对象%28可以复制或存储在容器%29中，但它们可以隐式转换为T&，以便它们可以用作参数，并具有接受基础类型的引用函数。
辅助函数std::ref和std::cref经常用于生成std::reference_wrapper物品。
std::reference_wrapper也用于将对象传递给std::bind的构造函数std::thread参考一下。
| std::reference_wrapper is guaranteed to be TriviallyCopyable. | (since C++17) |
|---|
成员类型
| type | definition |
|---|---|
| type | T |
| result_type(deprecated in C++17) | The return type of T if T is a function. Otherwise, not defined |
| argument_type(deprecated in C++17) | 1) if T is a function or pointer to function that takes one argument of type A1, then argument_type is A1. 2) if T is a pointer to member function of class T0 that takes no arguments, then argument_type is T0*, possibly cv-qualified 3) if T is a class type with a member type T::argument_type, then argument_type is an alias of that. |
| first_argument_type(deprecated in C++17) | 1) if T is a function or pointer to function that takes two arguments of type s A1 and A2, then first_argument_type is A1. 2) if T is a pointer to member function of class T0 that takes one argument, then first_argument_type is T0*, possibly cv-qualified 3) if T is a class type with a member type T::first_argument_type, then first_argument_type is an alias of that. |
| second_argument_type(deprecated in C++17) | 1) if T is a function or pointer to function that takes two arguments of type s A1 and A2, then second_argument_type is A2. 2) if T is a pointer to member function of class T0 that takes one argument A1, then second_argument_type is A1, possibly cv-qualified 3) if T is a class type with a member type T::second_argument_type, then second_argument_type is an alias of that. |
成员函数
| (constructor) | stores a reference in a new std::reference_wrapper object (public member function) |
|---|---|
| operator= | rebinds a std::reference_wrapper (public member function) |
| getoperator T& | accesses the stored reference (public member function) |
| operator() | calls the stored function (public member function) |
可能的实施
模板<class T>类引用[医]包装器{public：//type tydurifT type；//struction/Copy/destruction引用[医]包装器%28t和参%29不包括：[医]ptr%28std：：地址%28ref%29%29{}引用[医]包装器%28t&<；%29=删除；引用[医]包装器%28[医]包装器&%29 no以外=默认；//赋值引用[医]包装器和操作符=%28 const引用[医]包装器&x%29 no以外=默认；//访问操作符T&%28%29 constno，{Report]%2A[医]tr；}T&除{返回外，获取%28%29 Const no%2A[医]模板<class...。ArgTypes>TypeName STD：：Result[医]类型操作符%28%29%28 ArgTypes&&...args%29(返回STD：：Invoke%28get%28%29，std：：Forward)<ArgTypes>%28 args%29...%29；}私有：t%2A[医]PTR；}；
*。
例
演示引用的使用[医]包装器作为引用的容器，这使得使用多个索引访问同一个容器成为可能。
二次
#include <algorithm>
#include <list>
#include <vector>
#include <iostream>
#include <numeric>
#include <random>
#include <functional>
int main()
{
std::list<int> l(10
std::iota(l.begin(), l.end(), -4
std::vector<std::reference_wrapper<int>> v(l.begin(), l.end()
// can't use shuffle on a list (requires random access), but can use it on a vector
std::shuffle(v.begin(), v.end(), std::mt19937{std::random_device{}()}
std::cout << "Contents of the list: ";
for (int n : l) std::cout << n << ' '; std::cout << '\n';
std::cout << "Contents of the list, as seen through a shuffled vector: ";
for (int i : v) std::cout << i << ' '; std::cout << '\n';
std::cout << "Doubling the values in the initial list...\n";
for (int& i : l) {
i *= 2;
}
std::cout << "Contents of the list, as seen through a shuffled vector: ";
for (int i : v) std::cout << i << ' '; std::cout << '\n';
}
二次
可能的产出：
二次
Contents of the list: -4 -3 -2 -1 0 1 2 3 4 5
Contents of the list, as seen through a shuffled vector: -1 2 -2 1 5 0 3 -3 -4 4
Doubling the values in the initial list...
Contents of the list, as seen through a shuffled vector: -2 4 -4 2 10 0 6 -6 -8 8
二次
另见
| refcref (C++11)(C++11) | creates a std::reference_wrapper with a type deduced from its argument (function template) |
|---|---|
| bind (C++11) | binds one or more arguments to a function object (function template) |
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