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List:       kde-devel
Subject:    Re: OT: What is the purpose of virtual_hook anyways?
From:       Kuba Ober <kuba () mareimbrium ! org>
Date:       2005-01-21 18:47:08
Message-ID: 200501211347.08591.kuba () mareimbrium ! org
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On czwartek 20 styczeń 2005 11:21 am, David Faure wrote:
> On Thursday 20 January 2005 15:03, Jason Keirstead wrote:
> > Is it also to ensure BC, so that you have a generic entry point of data
> > into the class, in case you really need it?
>
> Yes. For internal additions of virtual methods. ( != adding virtual methods
> in public API, that can't be done )

Is adding virtual methods at the end of the class really a binary incompatible 
change? Why?

I mean, AFAIK, if done properly it will only enlarge the virtual table for 
given class. It won't move any previous items. 

I.e. consider an application compiled with following .h file (O):

class Test {
 virtual ~Test();

 void F1()
};

Then, you change it as follows (N):

class Test {
 virtual ~Test();

 void F1();
 virtual void F2();
};

The applications compiled with (O) header file won't have a way of referencing 
F2. The library compiled with (N) doesn't break apps compiled with (O). The 
apps compiled with (N) *and* referencing F2 will of course only work with (N) 
(or newer) libraries.

So, what's the catch?

Cheers, Kuba Ober
 
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