Re: Allocators and exceptions

[Markus E L <development-2006-8ecbb5cc8aREMOVETHIS@ANDTHATm-e-leypold.de>]

Stephen Leake wrote:

> Maciej Sobczak <see.my.homepage@gmail.com> writes:
>
>> On 11 Wrz, 11:16, "Dmitry A. Kazakov" <mail...@dmitry-kazakov.de>
>> wrote:
>>
>>> >>> P.S. Exceptions in constructors is a bad idea.
>>>
>>> > No, it's a very good idea. Otherwise you have to deal with half-baked
>>> > objects, which is Even Bigger Mess (tm).
>>>
>>> This is what you get when the exception is propagated out of a constructor.
>>
>> In this case I want the constructor to be rolled back.
>> Without exceptions (and rollback) the only option for handling errors
>> in initialization of (sub)components is to leave them half-baked.
>
> The point is that the constructor itself must do the roll-back, and
> leave the object in a consistent state.
>
> The rule should be:
>
>     Constructors should not propagate exceptions up; they must handle
>     all exceptions internally.

Forgive me that I contradict. The power of exceptions in a properly
designed language is, that it allows to handle problems during complex
object constructions, like

    T = new (something(new something_else ...)

and recover fully. Else we're back to testing failure after every step
again and manuall, as it was/is in C. Maybe I misunderstood the
problem altogether, though.

Regards --- Markus