Escape analysis

[Bill Baxter]

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.

--bb