From: Logan Capaldo <logancapaldo@...>
Date: 2006-09-11T11:48:59+09:00
Subject: Re: Struggling with Blocks

On Mon, Sep 11, 2006 at 11:15:23AM +0900, Paul Lutus wrote:
> Hal Fulton wrote:
> 
> > Paul Lutus wrote:
> >> 
> >> "do" reads from a list of items and provides them to its controlling
> >> block:
> >> 
> >> These two forms are interchangeable. One can argue that "do" is an
> >> implicit "{ ... }" block, or the reverse. But the point is "do" receives
> >> items and operates on them one at a time, then exits when its stream is
> >> empty.
> > 
> > Not strictly true.
> 
> Yes, strictly true, IMHO.
> 
> > Reemember that the iteration comes from the fact 
> > that the each method is invoking the block multiple times.
> 
> Not if there is only one item.
> 
> array = []
> 
> array << "one item"
> 
> array.each do |item|
>    # one item
> end
> 
> > 
> > Here's a do/end that will only execute once (and by the way
> > has no parameters):
> > 
> >    Dir.chdir(some_dir) do process_something end
> 
> In this example, "do" acts on its stream until it is empty. The stream
> happens to empty after one item, because that is what the stream contains.
> 
That's a bit of a stretch, don't you think? What exactly is in "the
stream"? I can pretty much gurantee you that Dir.chdir looks like:

def Dir.chdir(directory)
  old_directory = Dir.pwd
  begin
    chdir_without_block(directory)
    yield
  ensure
   chdir_without_block(old_directory)
  end
end

I see state, but no stream. What about instance_eval? That's not a
"stream" is it? Heck, lambda { |x, y| x + y }.call(1, 2), where's the
stream in that?