2019-06-14 C++ Destructor

For both user-defined or implicitly-defined destructors, after the body of the destructor is executed, the compiler calls the destructors for all non-static non-variant members of the class, in reverse order of declaration, then it calls the destructors of all direct non-virtual base classes in reverse order of construction (which in turn call the destructors of their members and their base classes, etc), and then, if this object is of most-derived class, it calls the destructors of all virtual bases.

在Destructor调用完成后，成员的Destructor调用前，this的状态是这样的：

如果在析构成员B时，使用了成员A，那么需要手动获取A的指针，而不是使用this捕获。因为这时的this已经是失效的了：

std::shared_ptr<A> dump_a = this->a;
this->b = std::shared_ptr<B>(this->a->CreateB(),
    [this, dump_a](B* p)
    {
        dump_a->ReleaseB(p); // OK
        this->a->ReleaseB(p); // Error
    });