From: Jacob Fugal <lukfugl@...>
Date: 2006-05-27T05:02:40+09:00
Subject: Re: Preserving Leading Zeros Using sprintf

On 5/26/06, Jeremy Smith <jeremy.smith@gmail.com> wrote:
> a=3
> b=8
> [a,b].collect! { |c| c = sprintf('%02d', c) }
> puts a # prints out 3 and not 03

You've been bit by the "variables == objects" mentality. When you
perform your #collect!, each *element* of the receiver of #collect! is
replaced by the result of the yield. See this:

  a = 3
  b = 8
  c = [a, b]
  c.collect! { |x| x = sprintf('%02d', x) }
  puts c[0] # prints '03'

So when #collect! operates on the first element, it's essentially as such:

  c[0] = sprintf('%02d', c[0])

This puts a *new* object in that slot of the array; it *doesn't* alter
the object that was previously in that slot. The variable a still
refers to the old object, not the new one.

Jacob Fugal