From: 7stud -- <lists@...>
Date: 2012-11-06T03:33:00+09:00
Subject: Re: Yield question

Assaf Shomer wrote in post #1082905:
> Ruby beginner here.
> I noticed the following code in the pickaxe book 1.9 page 101:
> ---------------------
> class VowelFinder
>  include Enumerable
>  def initialize(string)
>   @string = string
>  end
>  def each
>   @string.scan(/[aeiou]/) do |vowel|
>   yield vowel
>   end
>  end
> end
> --------------------
> What does it mean to have a *yield* inside a block?
>

'yield' calls a block.  Which block?  yield always calls the block that
was specified when calling 'the method'.  Which method?  The
method that contains the yield statement.  So, work your way outwards
from the yield statement until you find a def statement.  That is 'the
method' whose block(which is specified when calling the method) will be 
called by yield.

> Here the only yield is inside a block
> and there is no other method.

If yield wasn't allowed inside a block(e.g. a loop), which is inside a
method, then you would have to write methods like this:

def do_stuff
  yield 0
  yield 1
  #...
  #...
  yield 998
  yield 999
end


do_stuff {|x| puts x}

--output:--
1
2
998
999


But of course it makes sense to be able to do this:

def do_stuff
  1_000.times {|i| yield i}
end

do_stuff {|x| puts x}


--output:--
0
1
...
...
998
999

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