From: Robert Klemme <shortcutter@...>
Date: 2010-07-22T16:46:02+09:00
Subject: Re: Enumerators and generators

2010/7/22 Hal Fulton <rubyhacker@gmail.com>:
> I'm trying to grasp when/why one might use a generator instead of
> an enumerator (or vice versa).

It seems the alternative is Generator vs. Enumerable rather than
Generator vs. Enumerator.  Enumerator is rather a special form of
Enumerable which allows to do some things more efficiently because it
delays the iteration.  E.g.

# traditional one liner style: needs much memory:
matches = File.readlines("foo").select {|line| /keyword/ =~ line}

# Enumerator: only memory for the
matches = File.to_enum(:foreach, "foo").select {|line| /keyword/ =~ line}

# Same in 1.9 with implicit Enumerator creation
matches = File.foreach("foo").select {|line| /keyword/ =~ line}

It's a convenient replacement for the equally efficient (memory wise):

matches = []

File.foreach "foo" do |line|
  matches << line if /keyword/ =~ line
end

Generator is a completely different iteration style as Ricardo explained.

Kind regards

robert

-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/