From: Jamis Buck <jgb3@...>
Date: 2004-09-16T04:27:14+09:00
Subject: Re: Intercepting break within a block after yield

Alexey Verkhovsky wrote:
> Sorry for posting this without a subject earlier.
> 
> 
> ------------------------------------------------------------------------
> 
> Subject:
> No Subject
> From:
> Alexey Verkhovsky <alex@verk.info>
> Date:
> Thu, 16 Sep 2004 03:50:06 +0900
> To:
> ruby-talk@ruby-lang.org (ruby-talk ML)
> 
> To:
> ruby-talk@ruby-lang.org (ruby-talk ML)
> 
> 
> A question from Ruby-Forum:
> http://www.ruby-forum.org/bb/viewtopic.php?t=13
> 
> 
>>If I do this: 
>>
>>Code:
>>
>>a = [1, 2, 3] 
>>a.each do |x| 
>>  puts x 
>>  if x == 2 then break; end 
>>end 
>>
>>It works (prints 1, 2 then stops), but returns nil. Normally a.each
>>should return a. 
>>
>>I need an iterator that will return all elements processed until the
>>break. E.g. 
>>
>>Code:
>>
>>class Array 
>>  def each_with_a_twist 
>>    self.each_with_index do 
>>      |element, index| 
>>      yield element 
>>      >>> INTERCEPT THE BREAK <<< 
>>      break self[0, index] 
>>    end 
>>  end 
>>end 
>>
>>Is it possible?
> 
> 
> 
> I've come up with the following suggestion:
> 
> class A 
>   def a 
>     yield 
>     ensure puts "after block"; return 1 
>   end 
> end
> 
> I can see that this code is not good enough, because it doesn't
> differentiate between the block terminated by break and the block
> terminated by an error. What would be the Ruby Way here?
> 
> Alex
> 
> 
> 
> 

Would something like this work?

   class Array
     def each_with_a_twist
       index = 0
       return_list = true
       self.each_with_index do |element, index|
         yield element
       end
     rescue Exception
       return_list = false
       raise
     ensure
       return_list and return self[0..index]
     end
   end

   a = [ 1, 2, 3, 4, 5 ]
   result = a.each_with_a_twist { |i| break "blah" if i > 2 }
   p result

   result = a.each_with_a_twist { |i| raise "blah" if i > 2 }
   p result

-- 
Jamis Buck
jgb3@email.byu.edu
http://www.jamisbuck.org/jamis

"I use octal until I get to 8, and then I switch to decimal."