inheritance

问题 I am trying to understand the real requirement of the usage of templates for policy based design. Going through the new templated designs in C++ I found that policy based class design is a highly suggested way of design which allows you to 'plug-in' different behaviors from policy classes. A minimal example is the following (a shortened version of the wiki): template <typename LanguagePolicy> class HelloWorld : private LanguagePolicy { using LanguagePolicy::message; public: // Behaviour

问题 Does anyone know how to determine if the value of a WPF property is inherited? In particular, I'm trying to determine if the DataContext of a FrameworkElement was inherited from the parent or set directly on the element itself. 回答1: DependencyPropertyHelper.GetValueSource will give you a ValueSource, which includes a property for retrieving the BaseValueSource. The BaseValueSource enumeration tells you where the DependencyProperty is getting its value from, such as inherited from parent, set

问题 It seems as if that when I have an abstract base class that inherits from gevent.Greenlet (which inherits from the C extension module greenlet: https://github.com/python-greenlet/greenlet) then classes that implement it do not raise any of the abc errors about unimplemented methods. class ActorBase(gevent.Greenlet): __metaclass__ = abc.ABCMeta @abc.abstractmethod def foo(self): print "foo" class ActorBaseTest(ActorBase): def bar(self): print "bar" abt = ActorBaseTest() # no errors! If I

问题 It seems as if that when I have an abstract base class that inherits from gevent.Greenlet (which inherits from the C extension module greenlet: https://github.com/python-greenlet/greenlet) then classes that implement it do not raise any of the abc errors about unimplemented methods. class ActorBase(gevent.Greenlet): __metaclass__ = abc.ABCMeta @abc.abstractmethod def foo(self): print "foo" class ActorBaseTest(ActorBase): def bar(self): print "bar" abt = ActorBaseTest() # no errors! If I

问题 It seems as if that when I have an abstract base class that inherits from gevent.Greenlet (which inherits from the C extension module greenlet: https://github.com/python-greenlet/greenlet) then classes that implement it do not raise any of the abc errors about unimplemented methods. class ActorBase(gevent.Greenlet): __metaclass__ = abc.ABCMeta @abc.abstractmethod def foo(self): print "foo" class ActorBaseTest(ActorBase): def bar(self): print "bar" abt = ActorBaseTest() # no errors! If I

问题 It seems as if that when I have an abstract base class that inherits from gevent.Greenlet (which inherits from the C extension module greenlet: https://github.com/python-greenlet/greenlet) then classes that implement it do not raise any of the abc errors about unimplemented methods. class ActorBase(gevent.Greenlet): __metaclass__ = abc.ABCMeta @abc.abstractmethod def foo(self): print "foo" class ActorBaseTest(ActorBase): def bar(self): print "bar" abt = ActorBaseTest() # no errors! If I

问题 I have four classes. Request, DerivedRequest, Handler, DerivedHandler. The Handler class has a property with the following declaration: public abstract Request request { get; set; } The DerivedHandler needs to override this property so that it returns DerivedRequest instead: public override DerivedRequest request { get; set; } Does anyone have any ideas about how to make this work? 回答1: This isn't really a good way to structure things. Do one of the following 1) Just don't change the return

问题 I have four classes. Request, DerivedRequest, Handler, DerivedHandler. The Handler class has a property with the following declaration: public abstract Request request { get; set; } The DerivedHandler needs to override this property so that it returns DerivedRequest instead: public override DerivedRequest request { get; set; } Does anyone have any ideas about how to make this work? 回答1: This isn't really a good way to structure things. Do one of the following 1) Just don't change the return

问题 Please tell me what is of parent object instantiating with child class like: public class A { public A() { Console.WriteLine("A"); } public virtual void method() { Console.WriteLine("AM"); } } public class B : A { public B() { Console.WriteLine("B"); } public new void method() { Console.WriteLine("BM"); } public void method1() { Console.WriteLine("BM1"); } } class Program { static void Main(string[] args) { A obj = new B();// what is use of it? obj.method(); Console.Read(); } private void

问题 I know this question has been asked a lot, but the usual answers are far from satisfying in my view. given the following class hierarchy: class SuperClass{} class SubClass extends SuperClass{} why does people use this pattern to instantiate SubClass: SuperClass instance = new SubClass(); instead of this one: SubClass instance = new SubClass(); Now, the usual answer I see is that this is in order to send instance as an argument to a method that requires an instance of SuperClass like here: