From: David Alan Black <dblack@...>
Date: 2000-11-15T04:09:52+09:00
Subject: [ruby-talk:6367] Re: rescue clause affecting IO loop behavior

Hello again --

On Wed, 15 Nov 2000, ts wrote:

> >>>>> "D" == David Alan Black <dblack@candle.superlink.net> writes:
> 
> 
>  You don't have the same 'begin'
> 
> D>    begin
> D>      puts "Line from first block."
> D>    end until true
> 
>  With this 'begin' ruby don't test the first time. This mean that the block
>  is always executed once
> 
> D>    begin
> D>      puts "Line from second block."
> D>    rescue
> D>      d = "dummy exception handler"
> D>    end until true
> 
>  Here for ruby you don't have a block 'begin' but a block 'rescue'. This
>  mean that ruby will make the test before trying to enter in the block
>  'rescue'

I see what you mean, at least as far as the behavior goes.  But I don't see any
evidence of such a thing as a rescue block in the reference manual (1.4.6) -- only
optional rescue clauses, which occur inside begin/end blocks.

"Programming Ruby" also does not indicate that a begin/end block should act any
differently because it has one or more rescue clauses.  In discussing while/until
modifiers, it says:

  [given this: expression until boolean-expression]
  If expression is a begin/end block, the block will always be executed at least one time

and elsewhere: "Exceptions may be handled within the scope of a begin/end block."
There's no indication that putting a rescue clause in, or taking one out, will affect
the basic behavior of blocks (including begin...end until boolean).

I sort of hope it turns out to be a (fixable) problem in Ruby, rather than a
problem in the docs :-)  


David

-- 
David Alan Black
home: dblack@candle.superlink.net
work: blackdav@shu.edu
Web:  http://pirate.shu.edu/~blackdav