Re: [boost] [boost::throw_exception] and platforms where itdon't throw

From: Martin Bonner (martin.bonner_at_[hidden])
Date: 2005-12-09 04:47:13

----Original Message----
From: Peter Dimov [mailto:pdimov_at_[hidden]]
Sent: 08 December 2005 16:46
To: boost_at_[hidden]
Subject: Re: [boost] [boost::throw_exception] and platforms where
itdon't throw 

> Martin Bonner wrote:
>> From: Peter Dimov [mailto:pdimov_at_[hidden]]
>> 
>>> And of course in a situation where throw_exception is used to throw
>>> bad_alloc, an assertion makes even less sense, because there are no
>>> "logic errors" involved, and presenting the effects of a failed
>>> assertion to the end user would serve little purpose; the program
>>> could do nothing to defend itself from the out of memory situation.
>> 
>> But if a library is being used in an exception free environment,
>> maybe presenting an assertion failure to the user is as good as you
>> can do. 
> 
> Possibly, but who is "you" in the above sentence? 
The library author.

> The whole point of using an exception is that you the library
> author do not take responsibility of handling the error, leaving
> it up to you the library user to do that instead.
Right.  But the problem is what does the author of boost::whatever do when
the user wants to use boost::whatever in an environment that doesn't support
exceptions?  

One solution is to offer two functions (like at() and operator[]) and the
user who doesn't want exceptions uses the no-throw function.

That's a good solution sometimes, but there are other occasions where adding
all that extra machinery to support the few no-throw users is a bit much.
In those circumstances, it may be better for boost::whatever to say "if your
environment supports exceptions, you can handle condition  x by catching y;
if not, condition x will crash your program."  The no-throw users may decide
they know condition x is not going to happen, or that crashing is OK, or
that they can't use the library.  At least that way the users get to choose.

-- 
Martin Bonner
Martin.Bonner_at_[hidden]
Pi Technology, Milton Hall, Ely Road, Milton, Cambridge, CB4 6WZ,
ENGLAND Tel: [phone]