Re: Limitations of initialization list

From: Chris Theis (Christian.Theis_at_nospam.cern.ch)
Date: 08/31/04 

Date: Tue, 31 Aug 2004 17:51:00 +0200

"Marcin Kalicinski" <kalita@poczta.onet.pl> schrieb im Newsbeitrag
news:ch1vd8$fmn$1@korweta.task.gda.pl...
> Hi,
>
> Constructor of derived class needs to do some complex things before it
calls
> base class constructor. There is an ugly solution:
>
> bool ComplexThingToDo()
> {
> // ...
> return false; // dummy
> }
>
> class Derived: public Base
> {
> bool dummy;
> public:
> Derived(): dummy(ComplexThingToDo()), Base() { }
> };
>
> But I'm afraid that sequence of initializers in initialization list does
not
> enforce the actual sequence of execution. So this ugly solution will not
> work. Is there another way? Perhaps it is an example of bad design, doing
> some complex things before calling base class constructor?
>
> Best regards,
> Marcin
>

Naturally objects are constructed top to bottom in the inheritance tree.
However, you can enforce a specific order of executed base class ctors by
using multiple and virtual inheritance (see FAQ 25.14). This is a way to
solve your problem but still I have the itching feeling that you might have
a flaw in the design. Why can't the complex things be done by the base class
ctor? If they cannot but it is a problem if they are not yet done when the
base class ctor is executed then you might have a dependency of a base class
to a derived class and this is certainly a flaw. I don't suggest that this
is the case for you but you might consider rethinking your design.

Cheers
Chris

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