[dmd-internals] Throwing Errors

[Walter Bright]

On 3/15/2012 2:13 PM, Leandro Lucarella wrote:
> Walter Bright, el 14 de marzo a las 16:42 me escribiste:
>> On 3/12/2012 7:07 PM, Sean Kelly wrote:
>>> On Mar 12, 2012, at 5:35 PM, Walter Bright<walter at digitalmars.com>   wrote:
>>>
>>>> On 3/12/2012 2:39 PM, Sean Kelly wrote:
>>>>> On Mar 12, 2012, at 2:30 PM, Walter Bright wrote:
>>>>>> On 3/12/2012 12:34 PM, Sean Kelly wrote:
>>>>>>> I'm on the fence about whether attempting cleanup when an Error is thrown is desired behavior.  If there is no cleanup, why allow Errors to be caught at all?  We may as well simply call abort() at the point they're thrown.
>>>>>>>
>>>>>> So that an informative message can be printed, the backup engaged, attempt to shut down gracefully, log the failure details to a file, etc.
>>>>> … none of which may work if scope(exit) calls weren't run when the stack was unwound, since acquired mutexes would still be locked, etc.  I'd feel a lot less safe with having effectively done a longjmp across code that normally assumes finalization than with whatever the cause of the assertion did in the first place.
>>>>>
>>>> It's understood it may not work.
>>> So what's the reason to not call finalizers?
>> The program is corrupted at that point. The less code one attempts
>> to run, the better.
> Why? That's not always the case.

How do you know it's not the case for a particular instance? That's the problem.


>   And what could happen if you run
> cleanup code in a program that you say is completely invalid? So why
> would you care if the program gets more corrupted?

Because it can corrupt whatever external thing it is supposed to be doing.


> This is specially bad if a memory allocation fail is an Error. It
> basically forces you to check every allocation for a failure and
> translate it yourself to some kind of Exception if you are being careful
> to write some code that can survive to a memory allocation failure.

That sounds good in theory, but in practice, almost no program can recover from 
out of memory failure. Even those that pretend they can usually cannot because 
such was never tested.

> Why on earth do you want to make life miserable to people that have some
> valid use case for this, just to avoid corrupting a little more
> a program that's already corrupted.

I believe it is a *serious* mistake to believe one can recover a program that 
has become corrupted.

> Also adding special cases is ALWAYS confusing and error prone. Please,
> please, please don't make errors a broken special case, unless you have
> a very strong reason.
>

I do have a good reason.