Escape analysis

[Andrei Alexandrescu]

Bill Baxter wrote:
> On Wed, Oct 29, 2008 at 11:40 AM, Andrei Alexandrescu
> <SeeWebsiteForEmail at erdani.org> wrote:
>> Bill Baxter wrote:
>>> On Wed, Oct 29, 2008 at 7:23 AM, Sean Kelly <sean at invisibleduck.org>
>>> wrote:
>>>> Walter Bright wrote:
>>>>> Sean Kelly wrote:
>>>>>> I do think, however, that 'scope' should be the default behavior, for
>>>>>> two
>>>>>> reasons.  It's backwards-compatible, which is handy.  But more
>>>>>> importantly,
>>>>>> I'd say that probably 95% of the current uses of delegates are scoped,
>>>>>> and
>>>>>> that isn't likely to shift all the way to 50% even if D moved to a much
>>>>>> more
>>>>>> functional style of programming.  Algorithms, for example, all use
>>>>>> scoped
>>>>>> delegates, which I'd say is far and away their most common current use.
>>>>> The counter to that is that when there is an inadvertent escape of a
>>>>> reference, the error is often undetectable even while it silently
>>>>> corrupts
>>>>> data and behaves erratically.
>>>>>
>>>>> In other words (as Andrei pointed out to me) the cost of those errors,
>>>>> even though rare, is very high. This makes it highly desirable to
>>>>> prevent
>>>>> them automatically, rather than relying on the skill and attention to
>>>>> detail
>>>>> of the programmer.
>>>> I think the cost/benefit of this could probably be argued either way.
>>>> I've
>>>> never encountered a bug related to this, for example, so to me the
>>>> benefit
>>>> is entirely theoretical while the cost is immediate.
>>> I've had bugs caused by this but they were pretty easy to find.
>>> Some delegate I'm calling crashes and all the variables are
>>> nonsensical garbage...
>>> Hmm maybe I was using out-of-scope variables in that delegate that I
>>> wasn't supposed to?
>>>
>>> Maybe there are real cases where the bugs caused are harder to find.
>>> But I'll just add my 2c to Sean's.  I haven't had many such bugs, and
>>> when I've had them they've been pretty easy to find.
>> I don't think we can afford program correctness to rest on anecdote and "it
>> works for me". That age is long gone.
> 
> I haven't seen any real data about how serious a problem this is from
> you either.
> Chasing bogeymen is at least as bad as ignoring real problems.

Well to provide real data I'd have to spend time on user studies, which 
would be time-intensive. I also think it's not an interesting research 
problem because it is generally accepted in the community that memory 
un-safety is a source of problems. So I don't quite feel burdened with 
the need to provide a proof. Reframing the problem as chasing a bogeyman 
won't help with addressing it.

Andrei