std::as_const
From cppreference.com
Defined in header <utility>
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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
Run this code
#include <string> #include <cassert> #include <utility> #include <type_traits> int main() { std::string mutableString = "Hello World!"; auto&& constRef = std::as_const(mutableString); // mutableString.clear(); // OK // constRef.clear(); // error: 'constRef' is 'const' qualified, // but 'clear' is not marked const assert( &constRef == &mutableString ); assert( &std::as_const( mutableString ) == &mutableString ); using ExprType = std::remove_reference_t<decltype(std::as_const(mutableString))>; static_assert(std::is_same_v<std::remove_const_t<ExprType>, std::string>, "ExprType should be some kind of string." ); static_assert(!std::is_same_v<ExprType, std::string>, "ExprType 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) |