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Heres an example:

struct parent {
    int a;

    virtual void stuff() { a = 5; } //variant A
    void roundabout() { stuff(); }
    parent() { stuff(); }
};

struct child : parent {
    void stuff() override { a = 6; } //variant B
    child() : parent() {}
};

and usage

child c;  //calls variant A
auto p = reinterpret_cast<parent*>(&c);

c.stuff(); //calls variant B
c.roundabout(); //calls variant B
p->stuff(); //calls variant B
p->roundabout() //calls variant B

so after construction, any which way I call stuff() from inside or outside the class, without explicitly stating parent::stuff() I get child::stuff(), as expected.

The one exception is the constructor of parent that still calls parent::stuff() even though its triggered by the child constructor. This is really rather annoying since I have to include extra logic in the functions that the constructors call to make them behave as they should. Why is it like this?

user81993
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  • Note, the same issue also applies to the destructor as well. A parent class constructor cannot call virtual methods in the child class because the child class is not constructed until after the parent is constructed, and a parent class destructor cannot call virtual methods in the child class because the child has already been destructed before the parent is destructed. – Remy Lebeau Feb 24 '16 at 20:14

1 Answers1

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An instance of child cannot exist unless an instance of parent already exists. So in the constructor of parent, no instance of child can exist. So how could you call child::stuff if no child exists?

David Schwartz
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