From: Brian Candler <b.candler@...>
Date: 2008-12-17T00:17:18+09:00
Subject: Re: implementing python's os.walk

Brad Volz wrote:
> As some background, python's os.walk() [1] is a generator function.
> It is passed the top of a directory tree and it returns the following
> for each subdirectory that it encounters:
>    . the working directory
>    . an Array of subdirectories
>    . an Array of non-directory files

The normal 'ruby way' to do this would be as an object which *yields* 
each of these things in turn, rather than returning them.

In many cases you can use it directly like this. If you want to turn it 
into a generator you can wrap it using generator.rb; or more cleanly in 
ruby 1.9, turn it into an Enumerator, which has this functionality built 
in.

class Foo
  def all_dirs
    yield "dir1"
    yield "dir2"
    yield "dir3"
  end
end

foo = Foo.new

# Normal style
foo.all_dirs { |x| p x }

# Generator style (ruby 1.9, uses Fiber)
g = foo.to_enum(:all_dirs)
3.times { p g.next }

# Generator style (ruby 1.8, beware uses callcc)
require 'generator'
require 'enumerator'
g = Generator.new(foo.to_enum(:all_dirs))
3.times { p g.next }
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