“进口"从基类定义一个函数来实现抽象接口(C++ 中的多重继承) [英] "import" a definition of a function from a base class to implement abstract interface (multiple inheritance in C++)

问题描述

假设我们有一个继承自两个基类的类(多重继承).基class A是抽象的，声明了一个纯虚函数foo，另一个基class B声明并实现了一个函数foo完全相同的签名.

Say we have a class inheriting from two base classes (multiple inheritance). Base class A is abstract, declaring a pure virtual function foo, the other base class B declares and implements a function foo of the very same signature.

struct A
{
  virtual void foo(int i) = 0;
};

struct B
{
  virtual void foo(int i) {}
};

struct C : public A, public B {};

我想在派生的class C 中使用基础class B 的foo 实现.但是，如果我没有在派生的 class C 中第二次实现函数 foo，我将无法实例化它的任何对象(它仍然是抽象的).虚拟继承在这里没有预期的帮助(class A 和 class B 没有公共基类).

I want to use the implementation of foo from base class B in my derived class C. However, if I do not implement the function foo a second time in my derived class C, I cannot instantiate any object of it (it remains abstract). Virtual inheritance does not help here as expected (class A and class B have no common base class).

我想知道是否有一种方法可以将 foo 从 class B 的实现导入"到 class C 中，以免有重复相同的代码.

I wonder if there is a way to "import" the implementation of foo from class B into class C in order not to have to repeat the same code.

上面的例子当然是人为的.我想在 class B 中实现 foo 的原因是我想派生 class D : public B 并使用 class Bs foo 的实现.我知道继承(主要)不是为了代码重用，但我仍然希望以这种方式使用它.

Above example is of course contrived. The reason I want implement foo in class B is that I want to derive class D : public B and use class Bs implementation of foo. I know that inheritance is not (primarily) intended for code reuse, but I'd still like to use it in that way.

推荐答案

在 Java 中，您的示例代码有效.在 C++ 中它没有.这些语言之间的细微差别.

In java, your sample code works. In C++ it doesn't. A subtle difference between those languages.

您在 C++ 中的最佳选择是通过转发到 B::foo() 来定义 C::foo():

Your best option in C++ is to define C::foo() by forwarding to B::foo():

struct C : public A, public B
{
  virtual void foo(int i) { B::foo(i); }
};

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