std::is_const - cppreference.com
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      std::is_const

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      <tbody> </tbody>
      Definido no cabeçalho <type_traits>
      template< class T > struct is_const;
      		 (desde C++11)
      Se T é um tipo const qualificado (isto é, const ou const volatile), fornece o membro constante value true igual. Para qualquer outro tipo, é value false.
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      If T is a const-qualified type (that is, const, or const volatile), provides the member constant value equal true. For any other type, value is false.
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      Herdado de std::integral_constant

      Member constants

      value
      [estática]
      true se T is a const-qualified type , false contrário
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      true if T is a const-qualified type , false otherwise
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      (membro estático público constante)

      Member functions

      operator bool
      converte o objeto em bool, retorna value
      Original:
      converts the object to bool, returns value
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      (função pública membro)

      Member types

      Tipo
      Original:
      Type
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      		 Definition
      value_type bool
      type std::integral_constant<bool, value>

      Possível implementação

      template<class T> struct is_const          : std::false_type {};
template<class T> struct is_const<const T> : std::true_type {};

      Exemplo

      #include <iostream>
#include <type_traits>

int main() 
{
    std::cout << boolalpha;
    std::cout << std::is_const<int>::value << '\n';
    std::cout << std::is_const<const int>::value  << '\n';
}

      Saída: 

      false
true

      Veja também