Re: Ada 2005 puzzle

[Maciej Sobczak <see.my.homepage@gmail.com>]

W dniu piątek, 20 lipca 2012 14:49:14 UTC+2 użytkownik Dmitry A. Kazakov napisał:

> we = you and me?

Unfortunately, yes (although we want it for slightly different reasons, I guess).

[...]
> I meant here a different thing. If you have some dispatching operations to 
> be performed upon initialization,

I'm not sure what possible use-case would motivate it - I don't see any in the container's interface. Containers are not supposed to be more smart than necessary, they just have to keep objects.

> Let you have a hierarchy of types  T1:>T2:>T3. Then construction should run 
> as follows:
> 
> stage 1
> T1 constraints evaluation
> T2 constraints
> T3 constraints
> 
> allocation
> 
> stage 2
> T1 initialization
> T2 initialization
> T3 initialization
> 
> stage 3
> T1'Class initialization, only here we could dispatch on T1'Class
> T2'Class initialization
> T3'Class initialization
> 
> >> 1-3 cannot be effectively fused into single operation

Stage 3 is implicit, so we don't have to care, but I see the problem with 1 and 2.

> The technical reason IMO is that steps 1,2,3 are intermixed. This prevents 
> encapsulation of T1/1 + T1/2 + T1/3 into single subprogram.

Right - we would have to allow non-contiguous objects (multiple allocations for each component) and that would break the object model in almost all possible places.

-- 
Maciej Sobczak * http://www.msobczak.com * http://www.inspirel.com