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From: Hal Fulton on 22 Jul 2010 12:19
[Note: parts of this message were removed to make it a legal post.]

My next questions then are:

1. Does Enumerator::Generator have all the functionality of the
old generator.rb, just (it seems to me) a different usage?

2. In David's example, is "yielder" simply an array of objects? Do
we know or care? (If so, I'd be tempted to call it "list" because
"yielder" reminds of the keyword yield which I suppose is unrelated
here.)

Hal

On Thu, Jul 22, 2010 at 7:59 AM, Ricardo Panaggio <
panaggio.ricardo(a)gmail.com> wrote:

> On Thu, Jul 22, 2010 at 07:11, David A. Black <dblack(a)rubypal.com> wrote:
> > Hi --
> >
> > On Thu, 22 Jul 2010, Ricardo Panaggio wrote:
> >
> >> Hello Hal
> >>
> >> Generators "externalize" iteration, whereas Enumerator "internalize"
> >> it (but this docs may have already told you).
> >>
> >> Generators can be used to create a "controlled stream" of objects,
> >> that you can operate as you where using a remove control: go to the
> >> next (Generator#next), give me the position (Generator#pos), return to
> >> the beginning (Generator#rewind), ...
> >
> > Enumerators have #next and #rewind too, though (though not #pos). In
> > 1.9, as far as I can tell, the generator.rb library has been removed,
>
> I wasn't aware of it in 1.9. Good to now :)
>
> > and Generator is now a class inside Enumerator. An Enumerator::Generator
> > is created automatically, for the use of the enumerator, if you create
> > an enumerator with a block. Also, these Generators don't have #next and
> > friends; that's available via the enumerator. (I'm not sure what
> > happened to #pos.)
> >
> > As I understand it, the main thing about generators is that "controlled
> > stream" thing, where you can roll your own sense of iteration, rather
> > than just piggy-backing on what some enumerable object with its own
> > ideas about iteration thinks. Here's a (very contrived) 1.9 example:
> >
> > [dblack(a)ruby-versions ~]$ cat e.rb message = nil
> >
> > g = Enumerator::Generator.new do |yielder|
> > yielder << "Hi."
> > puts "I've been told to #{message}."
> > case message
> > when "leave"
> > yielder << "Bye."
> > when "stay"
> > yielder << "I'm still here!"
> > end
> > end
> >
> > e = Enumerator.new(g)
> >
> > puts e.next
> > message = "stay"
> > puts e.next
> >
> > e.rewind
> >
> > puts e.next
> > message = "leave"
> > puts e.next
> >
> > [dblack(a)ruby-versions ~]$ ruby e.rb Hi.
> > I've been told to stay.
> > I'm still here!
> > Hi.
> > I've been told to leave.
> > Bye.
> >
> >
> > David
> >
> > --
> > David A. Black, Senior Developer, Cyrus Innovation Inc.
> >
> > The Ruby training with Black/Brown/McAnally
> > Compleat Philadelphia, PA, October 1-2, 2010
> > Rubyist http://www.compleatrubyist.com
> >
> >
>
>

From: David A. Black on 22 Jul 2010 13:34
Hi --

On Fri, 23 Jul 2010, Hal Fulton wrote:

> My next questions then are:
>
> 1. Does Enumerator::Generator have all the functionality of the
> old generator.rb, just (it seems to me) a different usage?

No; it doesn't have #next or #rewind, but enumerators
(which can easily/transparently wrap generators) do. Neither of them
appears to have #pos, unless it's available in some other way that I
haven't spotted. (I'm writing this in haste and without benefit of irb,
so I'm not digging further right now.)

> 2. In David's example, is "yielder" simply an array of objects? Do
> we know or care? (If so, I'd be tempted to call it "list" because
> "yielder" reminds of the keyword yield which I suppose is unrelated
> here.)

It's actually an Enumerator::Yielder object, which I think only exists
for the purpose of being the receptacle for the objects to be yielded by
the generator.


David

--
David A. Black, Senior Developer, Cyrus Innovation Inc.

The Ruby training with Black/Brown/McAnally
Compleat Philadelphia, PA, October 1-2, 2010
Rubyist http://www.compleatrubyist.com

From: Roger Pack on 22 Jul 2010 15:29
Hal Fulton wrote:
> Hi, all...
>
> I'm trying to grasp when/why one might use a generator instead of
> an enumerator (or vice versa).
>
> I've used generators, but enumerators are newer to me.

Basically what was a Generator in 1.8 is now an enumerator in 1.9, and
faster.

http://wiki.github.com/rdp/ruby_tutorials_core/enumerator

Cheers!
-r
--
Posted via http://www.ruby-forum.com/.

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