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std::as_const_C++中文网

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

#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