Re: [boost] Interfaces Library, a macro less implementation

From: Joel de Guzman (joel_at_[hidden])
Date: 2005-07-02 18:21:18

Jonathan Turkanis wrote:

> I still haven't had time to think about Joel's proposal. However, I did spend
> consider effort at one point trying to support simple handwritten interfaces
> using ordinary member function syntax, and convinced myself that it was probably
> not possible. This might be because I had stronger requirements than Joel,
> though. Among other things, I required:
> 
> 1. support for derived interfaces, including MI
> 2. interface instance, including those involving MI, should have the size of a
> struct conatining two pointers (assuming the degree of EBO currently provided by
> most compilers)
> 3. It should be possible to define a const view const_view<IBar> of an
> interface, in which non-const functions are disabled. (Ordinary
> const-qualification is insufficient, since you can make a non-const copy of a
> const interface instance)
> 4. Implicit derived-to-base and non-const-to-const conversions
> 5. Support for aspect oriented programming.

Those are very good requirements.

> For 2 and 5 -- at least -- I concluded that interfaces need to contain a nested
> rebind-like structure which allows them to be reinstantiated with different base
> classes. Since it's redundant to implement an interface's infrastructure twice,
> I put the rebind stuff in a helper class, and made the actual interface derive
> from an appropriate specialization of rebind. I was unable to find any way for
> users to write this stuff by hand without going insane.
> 
> The template-based IDL looks like it is potentially the most usable. 

Given your requirements, I have to agree. Daniel Wallin's macro
based suggestion is also quite readable. The question now is:
when will they be implemented?

> The only
> open question is whether compile-times will suffer unduly.

That will only be answered when an implementation becomes available.
In the meantime, I'll see if I can get another shot at it following
your requirements.

Regards,
-- 
Joel de Guzman
http://www.boost-consulting.com
http://spirit.sf.net