multiple-inheritance | 易学教程

Virtual tables and memory layout in multiple virtual inheritance

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问题 Consider following hierarchy: struct A { int a; A() { f(0); } A(int i) { f(i); } virtual void f(int i) { cout << i; } }; struct B1 : virtual A { int b1; B1(int i) : A(i) { f(i); } virtual void f(int i) { cout << i+10; } }; struct B2 : virtual A { int b2; B2(int i) : A(i) { f(i); } virtual void f(int i) { cout << i+20; } }; struct C : B1, virtual B2 { int c; C() : B1(6),B2(3),A(1){} virtual void f(int i) { cout << i+30; } }; What\'s the exact memory layout of C instance? How many vptrs it

How does Python's “super” do the right thing?

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问题 I\'m running Python 2.5, so this question may not apply to Python 3. When you make a diamond class hierarchy using multiple inheritance and create an object of the derived-most class, Python does the Right Thing (TM). It calls the constructor for the derived-most class, then its parent classes as listed from left to right, then the grandparent. I\'m familiar with Python\'s MRO; that\'s not my question. I\'m curious how the object returned from super actually manages to communicate to calls of

Multiple Inheritance in java

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问题 Java is not allowing inheritance from multiple classes (still it allows inheritance from multiple interfaces.), I know it is very much inline with classic diamond problem. But my questions is why java is not allowing multiple inheritance like C++ when there is no ambiguity (and hence no chances of diamond problem) while inheriting from multiple base class ? 回答1: It was a design decision of Java. You'll never get it, so don't worry too much about it. Although MI might help you make Mixins,

What is the exact problem with multiple inheritance?

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I can see people asking all the time whether multiple inheritance should be included into the next version of C# or Java. C++ folks, who are fortunate enough to have this ability, say that this is like giving someone a rope to eventually hang themselves. What’s the matter with multiple inheritance? Are there any concrete samples? benjismith The most obvious problem is with function overriding. Let's say have two classes A and B , both of which define a method doSomething . Now you define a third class C , which inherits from both A and B , but you don't override the doSomething method. When

Can an interface extend multiple interfaces in Java?

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问题 Can an interface extend multiple interfaces in Java? This code appears valid in my IDE and it does compile: interface Foo extends Runnable, Set, Comparator<String> { } but I had heard that multiple inheritance was not allowed in Java. Why does there appear to be an exception for interfaces? 回答1: Yes, you can do it. An interface can extend multiple interfaces, as shown here: interface Maininterface extends inter1, inter2, inter3 { // methods } A single class can also implement multiple

Why exactly do I need an explicit upcast when implementing QueryInterface() in an object with multiple interfaces()

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问题 Assume I have a class implementing two or more COM interfaces: class CMyClass : public IInterface1, public IInterface2 { }; Almost every document I saw suggests that when I implement QueryInterface() for IUnknown I explicitly upcast this pointer to one of the interfaces: if( iid == __uuidof( IUnknown ) ) { *ppv = static_cast<IInterface1>( this ); //call Addref(), return S_OK } The question is why can\'t I just copy this ? if( iid == __uuidof( IUnknown ) ) { *ppv = this; //call Addref(),

How to avoid infinite recursion with super()?

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问题 I have code like this: class A(object): def __init__(self): self.a = 1 class B(A): def __init__(self): self.b = 2 super(self.__class__, self).__init__() class C(B): def __init__(self): self.c = 3 super(self.__class__, self).__init__() Instantiating B works as expected but instantiating C recursed infinitely and causes a stack overflow. How can I solve this? 回答1: When instantiating C calls B.__init__ , self.__class__ will still be C, so the super() call brings it back to B. When calling super(

Does C# support multiple inheritance?

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问题 A colleague and I are having a bit of an argument over multiple inheritance. I\'m saying it\'s not supported and he\'s saying it is. So, I thought that I\'d ask the brainy bunch on the net. 回答1: Nope, use interfaces instead! ^.^ 回答2: Sorry, you cannot inherit from multiple classes . You may use interfaces or a combination of one class and interface(s) , where interface(s) should be followed by class name in the signature. interface A { } interface B { } class Base { } class AnotherClass { }

How can I avoid the Diamond of Death when using multiple inheritance?

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问题 http://en.wikipedia.org/wiki/Diamond_problem I know what it means, but what steps can I take to avoid it? 回答1: A practical example: class A {}; class B : public A {}; class C : public A {}; class D : public B, public C {}; Notice how class D inherits from both B & C. But both B & C inherit from A. That will result in 2 copies of the class A being included in the vtable. To solve this, we need virtual inheritance. It's class A that needs to be virtually inherited. So, this will fix the issue:

How to make a Java class that implements one interface with two generic types?

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问题 I have a generic interface public interface Consumer<E> { public void consume(E e); } I have a class that consumes two types of objects, so I would like to do something like: public class TwoTypesConsumer implements Consumer<Tomato>, Consumer<Apple> { public void consume(Tomato t) { ..... } public void consume(Apple a) { ...... } } Apparently I can\'t do that. I can of course implement the dispatch myself, e.g. public class TwoTypesConsumer implements Consumer<Object> { public void consume