From: Shashank Date <sdate@...>
Date: 2004-01-19T06:15:03+09:00
Subject: Re: Newbie question re. blocks & variable scope


"Steve Cooper" <stevec890@yahoo.com> wrote in message
> I'd like to ask for some help with local variable scope.  I understand
> that the scope of a local variable is the "do...end" block in which it
> is created.

Correct (so far ;-) !

> However, the code below shows that the value assigned to
> the variable within a block does not persist after the single
> iteration in which the variable is given that value, although the
> variable is still defined in a later iteration.

Ah ha ! You are using the term _iteration_ to mean a
"looping construct" (control structure) and then in the example
using "each" which is an "iterator" (method).

In Ruby, a looping construct is _not the same_ as an iterator.
An iterator may be implemented using "yield" and some form
of a looping construct. This is nicely explained in Pickaxe.

> That is, in the idx=2  iteration, Ruby does not remember
> that a=11 in the previous iteration,
> but it also does not complain about an undefined local variable "a"
> (which it of course does outside the block).

Which is because you are using each (iterator).

> I haven't been able to
> find this behavior mentioned in the documentation or in this
> group--can you point me to something that will clarify for me what is
> going on?

Read the later half of  Chapter 7 of PickAxe carefully, esp. the sub-topics
"Loops" onwards.

> data=[1,2]
> data.each do | idx|
> if idx == 1
> a = 11
> print "idx=1: a=",a,"\n"
> elsif idx == 2
> b = 12
> print "idx=2: a=",a," b=",b,"\n"
> end
> end
> print "after:\n"
> print "a=",a," b=",b,"\n"


If you rewrite this using a _looping construct_ such as

#----------------------
data=[1,2]
for idx in data
  if (idx == 1)
    a = 11
    puts "idx=#{idx}: a=#{a}"
  elsif (idx == 2)
    b = 12
    p "idx=#{idx}: a=#{a} b=#{b}"
  end
end
#----------------------

then you should get the desired behavior.

Does that make sense ?

-- shanko