为什么虚拟基类必须由最派生的类构造?
以下代码无法编译:
class A {
public:
A(int) {}
};
class B: virtual public A {
public:
B(): A(0) {}
};
// most derived class
class C: public B {
public:
C() {} // wrong!!!
};
如果我在C的构造函数初始化列表中调用A的构造函数，即:
If I call A's constructor in C's constructor initialization list, that is:
// most derived class
class C: public B {
public:
C(): A(0) {} // OK!!!
};
确实有效.
显然，这是因为虚拟基类必须始终由大多数派生类构建.
Apparently, the reason is because virtual base classes must always be constructed by the most derived classes.
我不明白这个限制背后的原因.
I don't understand the reason behind this limitation.
推荐答案
因为它避免了这个:
class A {
public:
A(int) {}
};
class B0: virtual public A {
public:
B0(): A(0) {}
};
class B1: virtual public A {
public:
B1(): A(1) {}
};
class C: public B0, public B1 {
public:
C() {} // How is A constructed? A(0) from B0 or A(1) from B1?
};
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