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<?php interface A {} class B implements A {} class C {} class D extends C {} var_dump(in_array(A::class, class_implements(A::class))); var_dump(in_array(A::class, class_implements(B::class))); var_dump(in_array(A::class, class_implements(C::class))); var_dump(in_array(C::class, class_implements(D::class))); echo PHP_EOL; var_dump(is_a(A::class, A::class, true)); var_dump(is_a(B::class, A::class, true)); var_dump(is_a(C::class, A::class, true)); var_dump(is_a(D::class, C::class, true)); echo PHP_EOL; var_dump(is_subclass_of(A::class, A::class, true)); var_dump(is_subclass_of(B::class, A::class, true)); var_dump(is_subclass_of(C::class, A::class, true)); var_dump(is_subclass_of(D::class, C::class, true));