std::derived_from

 

哋它亢++

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Feature test macros (哋它亢++20)

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Concepts library (哋它亢++20)

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Technical specifications

Symbols index

External libraries

 

Concepts library

Core language concepts same_as derived_from convertible_to common_reference_with      common_with integral signed_integral unsigned_integral floating_point swappableswappable_with destructible constructible_from default_initializable move_constructible copy_constructible assignable_from

Comparison concepts equality_comparableequality_comparable_with totally_orderedtotally_ordered_with Object concepts movable copyable semiregular regular Callable concepts invocableregular_invocable predicate relation equivalence_relation strict_weak_order

Exposition-only concepts boolean-testable

 

Defined in header <concepts>
template< class Derived, class Base > concept derived_from =     std::is_base_of_v<Base, Derived> &&     std::is_convertible_v<const volatile Derived*, const volatile Base*>;		(since 哋它亢++20)

The concept derived_from<Derived, Base> is satisfied if and only if Base is a class type that is either Derived or a public and unambiguous base of Derived, ignoring cv-qualifiers.

Note that this behavior is different to std::is_base_of when Base is a private or protected base of Derived.

Example

Run this code

#include <concepts>
 
class A {};
 
class B : public A {};
 
class C : private A {};
 
// std::derived_from == true only for public inheritance or exact same class
static_assert(std::derived_from<B, B> == true);      // same class: true
static_assert(std::derived_from<int, int> == false); // same primitive type: false
static_assert(std::derived_from<B, A> == true);      // public inheritance: true
static_assert(std::derived_from<C, A> == false);     // private inheritance: false
 
// std::is_base_of == true also for private inheritance
static_assert(std::is_base_of_v<B, B> == true);      // same class: true
static_assert(std::is_base_of_v<int, int> == false); // same primitive type: false
static_assert(std::is_base_of_v<A, B> == true);      // public inheritance: true
static_assert(std::is_base_of_v<A, C> == true);      // private inheritance: true
 
int main() {}

See also

is_base_of (哋它亢++11)	checks if a type is derived from the other type (class template)
is_convertibleis_nothrow_convertible (哋它亢++11)(哋它亢++20)	checks if a type can be converted to the other type (class template)