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List:       ruby-talk
Subject:    [ruby-talk:29912] catch/throw (was  Proc.class vs yield)
From:       "Mark Hahn" <mchahn () facelink ! com>
Date:       2001-12-31 23:49:40
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> I haven't used Ruby's throw/catch yet and I don't plan to.

I'm curious.  What do you use to "break/retry/continue" inside a block?  It
always bothers me to have to use catch/throw in blocks.  I would love to
have an alternative.

-----Original Message-----
From: Mathieu Bouchard [mailto:matju@sympatico.ca]
Sent: Monday, December 31, 2001 2:26 PM
To: ruby-talk ML; Michael Lucas-Smith
Cc: ruby-talk ML
Subject: [ruby-talk:29907] Re: Proc.class vs yield



On Mon, 31 Dec 2001, Michael Lucas-Smith wrote:
> 	I'm a Smalltalk programmer and I have to say, of what I've seen of Ruby
> I'm impressed. I like it. Except for one inconsistency which really
> drives me up the wall. Two objects that nearly do the same thing, Proc
> and Block

Blocks are not the same thing. "block" is mostly a special (out-of-band)
parameter slot. This means that the block slot (&) is completely
separate from the optional (=) and rest (*) slots. Proc is the object type
and from the outside you can think of the block slot as holding a Proc
object: it doesn't matter that it's different under the hood, because you
don't see it.

I think I'd prefer Smalltalk-style [x|...] or Self-style (|x|...) to
Ruby's proc{|x|...}, even though there are nice advantages to the block
slot.

> I suspect you're right. In Smalltalk, every bit of code inside the [] is
> another object. They're always all full block closures. I have no idea
> what this does to the performance.

Lisp connoisseurs call it "slow" (but they also have lots of other ways
of expressing their contempt)

Anyway... it isn't clear to me that this can't be fixed. (disclaimer: i
don't know enough about compilers)

> I may be mistaken, but it appears as though the exception throwing and
> catching is global within your namespace? when I read 'catch' and
> 'throw' in the reference manuals for 1.4, they don't seem to talk about
> a scope at all.

Ruby's :foo is like Smalltalk's #foo or Lisp's :foo; so it's effectively
global. If you want something more flexible use raise/rescue, which work
with Exception objects. I haven't used Ruby's throw/catch yet and I don't
plan to.

________________________________________________________________
Mathieu Bouchard                   http://hostname.2y.net/~matju

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