std::as_const
来自cppreference.com
| 定义于头文件 <utility>
|
||
| template <class T> constexpr std::add_const_t<T>& as_const(T& t) noexcept; |
(1) | (C++17 起) |
| template <class T> void as_const(const T&&) = delete; |
(2) | (C++17 起) |
1) 将左值引用组成
t 的 const 类型2) 删除 const 右值引用重载，以禁止右值参数
可能的实现
template <class T> constexpr std::add_const_t<T>& as_const(T& t) noexcept { return t; } |
示例
运行此代码
#include <string> #include <cassert> #include <utility> #include <type_traits> int main() { std::string mutableString = "Hello World!"; const std::string& constView = std::as_const(mutableString); assert( &constView == &mutableString ); assert( &std::as_const( mutableString ) == &mutableString ); using WhatTypeIsIt = std::remove_reference_t<decltype(std::as_const(mutableString))>; static_assert(std::is_same<std::remove_const_t<WhatTypeIsIt>, std::string>::value, "WhatTypeIsIt should be some kind of string." ); static_assert(!std::is_same< WhatTypeIsIt, std::string >::value, "WhatTypeIsIt shouldn't be a mutable string." ); }
参阅
| (C++11) |
检查类型是否为 const 限定 (类模板) |
| (C++11)(C++11)(C++11) |
添加 const 或/与 volatile 限定符到给定类型 (类模板) |
| (C++11)(C++11)(C++11) |
从给定类型移除 const 或/与 volatile 限定符 (类模板) |
