| Defined in header <utility> | ||
|---|---|---|
template <class T> constexpr std::add_const_t<T>& as_const(T& t) noexcept; | (1) | (since C++17) |
template <class T> void as_const(const T&&) = delete; | (2) | (since C++17) |
1) Forms lvalue reference to const type of
t 2) const rvalue reference overload is deleted to disallow rvalue arguments
Possible implementation
template <class T>
constexpr std::add_const_t<T>& as_const(T& t) noexcept
{
return t;
} |
Example
#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." );
}See also
| (C++11) | checks if a type is const-qualified (class template) |
| (C++11)(C++11)(C++11) | adds const or/and volatile specifiers to the given type (class template) |
| (C++11)(C++11)(C++11) | removes const or/and volatile specifiers from the given type (class template) |
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