Re: Controlled types and exception safety

[Jean-Pierre Rosen <rosen@adalog.fr>]

Maciej Sobczak a �crit :

> 1. X is finalized. This allows me to clean up (free) its internal data.
> 2. Y is *shallow-copied* to X, so that in effect X and Y share their state.
> 3. X is adjusted. This allows me to duplicate its internal structure so 
> that it becomes independent from Y.
This is the simplistic view, which is sufficient in most cases.
The truth is slightly more complicated, see  7.6(11)

> I think that the inherent problem comes from the fact that the 
> finalization of X was forced *before* its adjustment.
> The canonical C++ way is to *first* make a copy of new value (because 
> this is when errors might occur, so that even if they occur, there was 
> no change in the destination object) and *then* inject the duplicate 
> into the destination object, getting rid of its old state (and this is 
> assumed to be nothrow).
This is the way it actually works in Ada, unless the compiler proves 
that the intermediate object can be eliminated. In your case, it cannot.

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            J-P. Rosen (rosen@adalog.fr)
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