Enumerators and generators
in [Ruby]
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From: Hal Fulton on 21 Jul 2010 21:12 [Note: parts of this message were removed to make it a legal post.] 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. I've heard one person's take on this (thanks David!) but thought I might ask more thoughts... Thanks, Hal Fulton
From: Ricardo Panaggio on 21 Jul 2010 21:43 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), ... Enumerator offers methods to iterate through the entire stream, like iterate using a windows of size X (Enumerator#each_cons), iterate using slices from the stream (Enumerator#each_slide), ... They are quite different in use, although both are usable to iterate over data. On Wed, Jul 21, 2010 at 22:12, Hal Fulton <rubyhacker(a)gmail.com> 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. > > I've heard one person's take on this (thanks David!) but thought > I might ask more thoughts... > > Thanks, > Hal Fulton >
From: Robert Klemme on 22 Jul 2010 03:46 2010/7/22 Hal Fulton <rubyhacker(a)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/
From: David A. Black on 22 Jul 2010 06:11 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, 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: Ricardo Panaggio on 22 Jul 2010 08:59
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 > > |