From: Dave Cantrell <ruby-talk@...>
Date: 2006-02-15T15:05:17+09:00
Subject: Re: Rescuing blocks?

Hal Fulton wrote:
> Dave Cantrell wrote:
>> Eric Hodel wrote:
>>
>>>
>>> You're going to get a performance hit setting up an exception trap 
>>> this way.
>>
>> Time for some down-South edumucation. What kind of performance hit are 
>> we talking about here? And why the hit at all?
>>
>> (I seem to recall reading somewhere once upon a time about memory 
>> stack stuff, but I'm not an old-school C-programmer so I never had to 
>> deal with it --- unfortunately for me...)
> 
> Well, my knowledge is limited. Someone else can answer better.
> 
> But look at it from a common-sense standpoint. Exceptions aren't
> magic. Everything Ruby does can be done in assembly language, it's
> just more verbose.
> 
> I would think that exceptions, at the lowest level, work something
> like:
> 
>    if something_happened_here
>       goto the_place_where_exceptions_are_caught
> 
> So at the very least, catching exceptions means that you're doing
> some sort of comparison or conditional branch. And this is code
> that doesn't have to be run/generated *unless* you are catching
> exceptions.
> 
> Just my naive take.
> 
> 
> Hal
> 
> 
> 

That's kind of along the lines of what I was thinking, just better said. 
But this makes me wonder:

(a) Worrying about the performance hit from comparison/conditional 
branching leads to the question "is all branching in blocks bad?" 
Obviously not.

(b) Couldn't you say that *any* conditional could be jumping out to 
another section of code? i.e. not just exception handlers?

   if this_is_true
      goto where_we_do_stuff_when_this_is_true

Hmm. This is something I've read, and it's in my brain somewhere, but I 
don't know it well enough to grok it yet.

Especially at midnight... :(

But your explanation gives me a better idea of what is happening, even 
with my questions.

Thanks!
-dave