Delegation and Calling Parent Class Constructors: How do I do both?

Question

I was wondering something, regarding delegation of derived class constructors. What's the proper method for delegating constructors when you also have to call the parent class' constructor? I know you can't have both delegation and member initialisation in the same initialiser list, but I don't know if calling the parent class' constructor has the same limitation.

// Option 1: Call parent class constructor, then delegate:

class Foo {
    public:
        Foo(int);
};

class Bar : public Foo {
    public:
        Bar(int, float) : Foo(int), Bar(int, float, 'c');
        Bar(int, float, char);
};

// Option 2: Delegate, then call parent class constructor:

class Foo {
public:
    Foo(int);
};

class Bar : public Foo {
    public:
        Bar(int, float) : Bar(int, float, 'c'), Foo(int);
        Bar(int, float, char);
};

// Option 3: Primary constructor calls parent class constructor:

class Foo {
    public:
        Foo(int);
};

class Bar : public Foo {
    public:
        Bar(int, float) : Bar(int, float, 'c');
        Bar(int, float, char) : Foo(int);
};

I would assume it's either #1 or #3 (most likely #3), but I'm not sure; I know it's not a combination, since that would call Foo() twice. I don't think it's #2, but I listed it just to cover all the possibilities.

I know there's a bit of a weird property to delegation in C++, too, in that the class is considered to be constructed as soon as any of its constructors finishes executing, even if you delegated the call to a different one and it hasn't finished the one that was actually [i]called[/i] yet. I don't think that would have any effect in this case, but it's worth mentioning.

I searched the site and googled it, but couldn't find an exact answer; the closest I could find was the bit about not having delegation and initialisation in the same init list, on MSDN. I'm unable to run some test code through a fully C++11-compatible compiler right at the moment, so I couldn't just experiment. Help would be appreciated.

Thanks in advance.

Answer 1

Option #3 is the only valid one. You can't have a base initializer and a delegation in the same init list for the same reason you can't have a member initializer and a delegation: how would the compiler know not to initialize the member/base twice?

Answer 2

This is the only valid option:

class Bar : public Foo {
    public:
        Bar(int, float) : Bar(int, float, 'c') {}
        Bar(int, float, char) : Foo(int) {}
};

If your constructor delegates, then its mem-initializer-list is allowed to only consist of the single delegating constructor call.