From: "Hal E. Fulton" <hal9000@...>
Date: 2001-11-16T13:47:01+09:00
Subject: [ruby-talk:25383] Arrays, iterators, and map/collect

Hello all...

This may be two or more questions.
My thoughts are a little disorganized. :)

Sometimes I want to do something to
each item in an array. An iterator seems
natural for this (to me).

  strings = %w[ alpha beta gamma ]
  strings.each { |s| s << ".post" }

This works because << operates on the
object, not the variable. But if I do this:

  strings.each { |s| s = "pre." + s }

obviously it doesn't work because we're
creating a new object.

On the other hand, map! (or collect!) will
do this just fine.

  strings.map! { |s| s = "pre." + s }

But what if I want to do an operation 
conditionally? Is this still a good way to do it,
in a case where the mapped value is
sometimes/always the same as the original?

  strings.map! { |s| if s[0]==?a then s else "pre." + s end }

This, of course, doesn't work:

  strings.each do |s|
    s = "pre." + s if s[0] != ?a
  end

I really don't like the case where each_with_index
is used and the array is referenced inside the block
of its own iterator. (Sometimes I do it, though, depending
on circumstances.)

  strings.each_with_index do |s,i|
    strings[i] = "pre." + s if s[0] != ?a
  end

The above works, but seems ugly.

Comments, anyone?

Hal