Movatterモバイル変換


[0]ホーム

URL:


cppreference.com
Namespaces
Variants
    Actions

      std::is_polymorphic

      From cppreference.com
      <cpp‎ |types
       
       
      Metaprogramming library
      Type traits
      Type categories
      (C++11)
      (C++11)(DR*)
      (C++11)
      (C++11)
      (C++11)
      (C++11)
      (C++11)
      (C++11) 
      Type properties
      (C++11)
      (C++11)
      is_polymorphic
      (C++11)
      (C++14)
      (C++11)(deprecated in C++26)
      (C++11)(until C++20*)
      (C++11)(deprecated in C++20)
      (C++11)
      Type trait constants
      Metafunctions
      (C++17)
      Supported operations
      Relationships and property queries
      Type modifications
      Type transformations
      (C++11)(deprecated in C++23)
      (C++11)(deprecated in C++23)
      (C++11)
      (C++11)(until C++20*)(C++17)

      Compile-time rational arithmetic
      Compile-time integer sequences
       
      Defined in header<type_traits>
      template<class T>
      struct is_polymorphic;
      (since C++11)

      std::is_polymorphic is aUnaryTypeTrait.

      IfT is apolymorphic class (that is, a non-union class that declares or inherits at least one virtual function), provides the member constantvalue equal totrue. For any other type,value isfalse.

      IfT is an incomplete non-union class type, the behavior is undefined.

      If the program adds specializations forstd::is_polymorphic orstd::is_polymorphic_v, the behavior is undefined.

      Contents

      [edit]Template parameters

      T - a type to check

      [edit]Helper variable template

      template<class T>
      constexprbool is_polymorphic_v= is_polymorphic<T>::value;
      (since C++17)
      [edit]

      Inherited fromstd::integral_constant

      Member constants

      value
      [static]
      true ifT is apolymorphic class type,false otherwise
      (public static member constant)

      Member functions

      operator bool
      converts the object tobool, returnsvalue
      (public member function)
      operator()
      (C++14)
      returnsvalue
      (public member function)

      Member types

      Type Definition
      value_typebool
      typestd::integral_constant<bool, value>

      [edit]Possible implementation

      namespace detail{template<class T>std::true_type detect_is_polymorphic(        decltype(dynamic_cast<constvolatilevoid*>(static_cast<T*>(nullptr))));template<class T>std::false_type detect_is_polymorphic(...);}// namespace detail template<class T>struct is_polymorphic: decltype(detail::detect_is_polymorphic<T>(nullptr)){};

      [edit]Example

      Run this code
      #include <type_traits> struct A{int m;};static_assert(!std::is_polymorphic_v<A>); struct B{virtualvoid foo();};static_assert(std::is_polymorphic_v<B>); struct C: B{};static_assert(std::is_polymorphic_v<C>); struct D{virtual ~D()=default;};static_assert(std::is_polymorphic_v<D>); // Uses inheritance, but not the virtual keyword:struct E: A{};static_assert(!std::is_polymorphic_v<E>); struct F:virtual A{};static_assert(!std::is_polymorphic_v<F>); struct AX: A{};struct AY: A{};struct XY:virtual AX,virtual AY{};static_assert(!std::is_polymorphic_v<XY>); int main(){}

      [edit]Defect reports

      The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

      DRApplied toBehavior as publishedCorrect behavior
      LWG 2015C++11the behavior was undefined if
      T is an incomplete union type
      the base characteristic is
      std::false_type in this case

      [edit]See also

      (C++11)
      checks if a type is a non-union class type
      (class template)[edit]
      checks if a type is an abstract class type
      (class template)[edit]
      checks if a type has a virtual destructor
      (class template)[edit]
      Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/types/is_polymorphic&oldid=159388"

      [8]ページ先頭

      ©2009-2025 Movatter.jp