Exception/Error division in D

[Steven Schveighoffer]

On Thu, 24 May 2012 15:33:07 -0400, Sean Kelly <sean at invisibleduck.org>  
wrote:

> On May 24, 2012, at 11:39 AM, Steven Schveighoffer wrote:
>

>>> Can "Out of memory" be an Error? No, because e.g. if I read a user  
>>> file that require me to create a large array (> 100 MiB, e.g.) I don't  
>>> want to crash, but just tell, that "Dear user, the file can't be  
>>> opened because it requires..."
>>
>> Right, out of memory is only an error if your program's invariant  
>> depends on the memory allocation.  You can plan for the above easily  
>> enough, but not realistically for all tasks and all library code that  
>> require allocation.
>>
>> For example, let's say you are restructuring a hash table, and you  
>> reallocate some nodes.  You have half transferred over the old  
>> structure to the new structure, and you run out of memory.  How to  
>> recover from this?
>
> I think it's fair to expect code that allocates be exception-safe in the  
> face of allocation errors.  I know I'm always very careful with  
> containers so that an allocation failure doesn't result in corruption,  
> for example.

I don't think it's fair to expect *all* code to be able to safely recover  
 from an out of memory exception.  I pretty much *never* write code that  
worries about out of memory errors.  One cannot always expect an operation  
involving hundreds of allocations to be atomic.

That being said, we should provide a mechanism so you can handle it, as  
it's reliably detectable and very recoverable in many situations.

-Steve