Escape analysis

[Bill Baxter]

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.

--bb