Escape analysis

[Andrei Alexandrescu]

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.

Andrei