std::as_const (3) - Linux Man Pages

std::as_const: std::as_const

NAME

std::as_const - std::as_const

Synopsis


Defined in header <utility>
template <class T> (1) (since C++17)
constexpr std::add_const_t<T>& as_const(T& t) noexcept;
template <class T> (2) (since C++17)
void as_const(const T&&) = delete;


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!";
      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


is_const checks if a type is const-qualified
                (class template)
(C++11)


add_cv
add_const
add_volatile adds const or/and volatile specifiers to the given type
                (class template)
(C++11)
(C++11)
(C++11)


remove_cv
remove_const
remove_volatile removes const or/and volatile specifiers from the given type
                (class template)
(C++11)
(C++11)
(C++11)