multiple-inheritance

问题 When I see code snippets like interface A { void a(); void b() default { System.out.println("b"); }; void c() final { System.out.println("c"); }; } I have one question. Haven't we already got enough sh*t in Java? Why one might need this? 回答1: I suggest you to look at this conference : http://medianetwork.oracle.com/media/show/16999 This explain everything. The most interesting thing to do is to allow an interface to evolve without rewritting your whole codebase. This is key to allow a big

问题 Is it possible to create a class that inherits from multiple instances of namedtuple, or create something to the same effect (having an immutable type that combines the fields of the base types)? I haven't found a way to do so. This example illustrates the problem: >>> class Test(namedtuple('One', 'foo'), namedtuple('Two', 'bar')): >>> pass >>> t = Test(1, 2) TypeError: __new__() takes 2 positional arguments but 3 were given >>> t = Test(1) >>> t.foo 1 >>> t.bar 1 The problem seems to be that

问题 I have this code, showing a classic diamond pattern: class A: def __init__( self, x ): print( "A:" + x ) class B( A ): def __init__( self, x ): print( "B:" + x ) super().__init__( "b" ) class C( A ): def __init__( self, x ): print( "C:" + x ) super().__init__( "c" ) class D( B, C ): def __init__( self ): super().__init__( "d" ) d = D() The output is: B:d C:b A:c B:d makes sense, since D derives from B . The A:c I almost get, though I could equally see A:b . However, the C:b bit doesn't make

问题 I'm using variadic templates with multiple virtual inheritance in C++ to aggregate types into a single structure definition. Here is a sample set of structures: struct meas { int i; }; struct meas2 : public virtual meas { int j; }; struct meas3 : public virtual meas { int k; }; I then aggregate these using multiple virtual inheritance: template <typename... Args> struct zipper : public virtual Args... {}; I can then do: typedef zipper<meas, meas2> meas_type; meas* m = new meas_type; These can

问题 The following code generates warning C4250. My question is, what's the best solution to it? class A { virtual void func1(); } class B : public A { } class C : public A { virtual void func1(); } class D : public B, public C { } int main() { D d; d.func1(); // Causes warning } According to what I've read it should be possible to do this: class D : public B, public C { using B::func1(); } But, this doesn't actually do anything. The way I've currently solved it is: class D : public B, public C {

问题 Given the following code (without virtual inheritance) : class A { public: virtual void f() = 0; }; class B : public A { public: virtual void f() {} }; class C : public A { public: virtual void f() {} }; class D : public B, public C { /* some code */ }; int main() { D d; return 0; } the code compile. On the other hand , here : class A { public: virtual void f() = 0; }; class B : virtual public A { virtual void f() {} }; class C : virtual public A { virtual void f() {} }; class D : public B,

问题 Given the following code (without virtual inheritance) : class A { public: virtual void f() = 0; }; class B : public A { public: virtual void f() {} }; class C : public A { public: virtual void f() {} }; class D : public B, public C { /* some code */ }; int main() { D d; return 0; } the code compile. On the other hand , here : class A { public: virtual void f() = 0; }; class B : virtual public A { virtual void f() {} }; class C : virtual public A { virtual void f() {} }; class D : public B,

问题 I'm writing some code involving inheritance from a basic ref-counting pointer class; and some intricacies of C++ popped up. I've reduced it as follows: Suppose I have: class A{}; class B{}; class C: public A, public B {}; C c; C* pc = &c; B* pb = &c; A* pa = &c; // does pa point to a valid A object? // does pb point to a valid B object? // does pa == pb ? Furthermore, does: // pc == (C*) pa ? // pc == (C*) pb ? Thanks! 回答1: does pa point to a valid A object? does pb point to a valid B object?

问题 I have 2 classes one includes methodA and the other include methodB. So in a new class I need to override the methods methodA and methodB. So how do I achieve multiple inheritance in objective C? I am little bit confused with the syntax. 回答1: Objective-C doesn't support multiple inheritance, and you don't need it. Use composition: @interface ClassA : NSObject { } -(void)methodA; @end @interface ClassB : NSObject { } -(void)methodB; @end @interface MyClass : NSObject { ClassA *a; ClassB *b; }

问题 Say I have a multiple inheritance scenario: class A(object): # code for A here class B(object): # code for B here class C(A, B): def __init__(self): # What's the right code to write here to ensure # A.__init__ and B.__init__ get called? There's two typical approaches to writing C 's __init__ : (old-style) ParentClass.__init__(self) (newer-style) super(DerivedClass, self).__init__() However, in either case, if the parent classes ( A and B ) don't follow the same convention, then the code will