Question

如果存在这样的事情，我会遇到一种“三角继承”问题。基本上，我有一个定义接口的抽象基类，以及一个定义该接口的 part 的实现的策略类，如下所示：

class SystemA : public System, public SomethingImplementation {/*...*/};
class SystemB : public System, public SomethingImplementation {/*...*/};
class SystemC : public System, { /* with a custom implementation ... */ };

然后我为不同的情况提供了几种接口实现。在某些情况下，我想使用简单的实现，而在其他情况下，我想要自定义它们

59:13: error: cannot declare variable 'a' to be of abstract type 'SystemA'
22:7: note:   because the following virtual functions are pure within 'SystemA':
6:18: note:     virtual void System::doSomething()
7:18: note:     virtual bool System::somethingDone() const
60:13: error: cannot declare variable 'b' to be of abstract type 'SystemB'
31:7: note:   because the following virtual functions are pure within 'SystemB':
6:18: note:     virtual void System::doSomething()
7:18: note:     virtual bool System::somethingDone() const
63:38: error: invalid new-expression of abstract class type 'SystemA'

我无法弄清楚SystemA或SystemB类的细节可能会使实现工作

https://blog.kapeli.com/dash-3-dot-4

解决方案1 

使用语句，在这种情况下似乎没有做任何事情。

http://cpp.sh/73r5

SomethingInterface

解决方案2

添加额外的接口类。创建Interface类，并从SomethingImplementation继承SomethingInterface和$('a.some-link-class').click(function(e) { e.preventDefault(); if ($(window).width() < 1000) window.location = 'http://small-screen-url/'; else window.location = window.location = 'http://large-screen-url/'; });。这会将问题变成一个常规的“钻石继承”问题，但我似乎仍然无法让编译器做我想做的事。

http://cpp.sh/2nhki

将另一个类的实现用于父类的虚方法有什么方法？

Answer 1

我相信你想做这样的事情。

// The interface.
class IInterface
{
public:
    virtual ~IInterface() {}
    virtual void method1() = 0;
    virtual void method2() = 0;
};

// A partial, abstract implementation of interface.
// This base class implements method1 but leaves method2 unimplemented,
// which means this class cannot be instantiated.
class PartialImplementation : public IInterface
{
public:
    virtual void method1() {}
};

// Full implementation that uses the partial implementation above.
// method1's implementation is from the base class.
// method2's implementation is in this class.
// Because all methods are implemented (directly or inherited), this class can be instantiated.
class FullImplementation1 : public PartialImplementation
{
public:
    void method2() {}
};

// Full implementation that uses the partial implementation above.
// method1's implementation is in this class (overrides base implementation).
// method2's implementation is in this class.
// Because all methods are implemented (directly), this class can be instantiated.
class FullImplementation2 : public PartialImplementation
{
public:
    void method1() {}
    void method2() {}
};

// Full implementation that DOES NOT use the partial implementation above.
// method1's implementation is in this class.
// method2's implementation is in this class.
// Because all methods are implemented (directly), this class can be instantiated.
class FullImplementation3 : public IInterface
{
public:
    void method1() {}
    void method2() {}
};

int main()
{
    FullImplementation1 i1; // OK
    FullImplementation2 i2; // OK
    FullImplementation3 i3; // OK

    IInterface* p1 = new FullImplementation1(); // OK
    delete p1; // OK

    IInterface* p2 = new FullImplementation2(); // OK
    delete p2; // OK

    IInterface* p3 = new FullImplementation3(); // OK
    delete p3; // OK

    return 0;
}

Answer 2

我所看到的钻石继承的每个例子都来自糟糕的设计，因为对IS-A和HAS-A关系的误解。不要继承使用实现，继承提供实现（例如继承实现）。

SystemA应该从System继承，并且SomethingImplementation作为其所调用方法的成员。

您也可以查看mixins。

我可以使用另一个父类的虚方法实现吗？

2 个答案: