How to use Enumerator::Generator in Ruby 1.9.2

ruby-talk
1

Hi everybody,

There's a class called Enumerator::Generator in Ruby 1.9.2, and it seems
to have only one method "#each" of its own.
However the ruby-doc page of Enumerator::Generator is empty, I didn't
google out the useage of it.

So, can you give me an example how to use this class?

Thank you!

Joey

···

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Posted via http://www.ruby-forum.com/.

2

You can see an example in a recent posting:

http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/381414

Cheers

robert

···

On Tue, Apr 19, 2011 at 8:43 AM, Joey Zhou <yimutang@gmail.com> wrote:

Hi everybody,

There's a class called Enumerator::Generator in Ruby 1.9.2, and it seems
to have only one method "#each" of its own.
However the ruby-doc page of Enumerator::Generator is empty, I didn't
google out the useage of it.

So, can you give me an example how to use this class?

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

3

e = Enumerator.new do |y|
  y << 1
end

p e #=> #<Enumerator: #<Enumerator::Generator:0x1345b00>:each>

well, it seems that e is an Enumerator, but has an Enumerator::Generator
in it. I am confused what on earth Enumerator::Generator is. Can I get
an object that can return "Enumerator::Generator" if I type "obj.class"?

···

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4

May I think like this, Enumerator.new is a short way, including two
steps:

eg = Enumerator::Generator.new {|y| y << 1 }
p eg # #<Enumerator::Generator:0xb44890>
e1 = Enumerator.new(eg)
p e1 # #<Enumerator: #<Enumerator::Generator:0xb44890>:each>

e2 = eg.to_enum
p e2 # #<Enumerator: #<Enumerator::Generator:0xb44890>:each>

so ruby-doc says there are two forms of Enumerator.new:

Enumerator.new(obj, method = :each, *args)
Enumerator.new { |y| ... }

in fact, there's just one, the second one can be regarded as

Enumerator.new(enum_generator_instance)

Does Enumerator::Generator exist, because Ruby 1.8 has a Generator
class?

···

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5

But this can be achieved easier, as e.g. (0..9).cycle already returns an Enumerator.

ruby-1.9.2-p136 :002 > foo = (0..9).cycle
  => #<Enumerator: 0..9:cycle>
ruby-1.9.2-p136 :003 > foo.next
  => 0
ruby-1.9.2-p136 :004 > foo.take 12
  => [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1]
ruby-1.9.2-p136 :005 > foo.next
  => 1
ruby-1.9.2-p136 :006 >

···

On 19.04.2011 09:44, Robert Klemme wrote:

You can see an example in a recent posting:
http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/381414

--
Gruß, Johannes

6

Joey Zhou wrote in post #993744:

e = Enumerator.new do |y|
  y << 1
end

p e #=> #<Enumerator: #<Enumerator::Generator:0x1345b00>:each>

well, it seems that e is an Enumerator, but has an Enumerator::Generator
in it. I am confused what on earth Enumerator::Generator is.

It's that y thing, and it knows how to provide values to the enumerator
when your code requests values from the enumerator.

Can I get
an object that can return "Enumerator::Generator" if I type "obj.class"?

Let's see:

1)
obj = Enumerator::Generator.new
puts obj.class

--output:--
prog.rb:1:in `initialize': no block given (LocalJumpError)
  from prog.rb:1:in `new'
  from prog.rb:1:in `<main>'

2)
obj = Enumerator::Generator.new do |y|
  y << 1
end

puts obj.class

--output:--
Enumerator::Generator

There you go.

···

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7

Yes, but please note that #cycle was not used in the example posted by
me which I was referring to. Any simple example can usually be solved
with another approach than Enumerator so I guess most examples which
are good for conveying functionality of Enumerator.new will suffer
from that very same issue. :slight_smile:

Kind regards

robert

···

On Tue, Apr 19, 2011 at 12:55 PM, Johannes Held <johannes.held@informatik.uni-erlangen.de> wrote:

On 19.04.2011 09:44, Robert Klemme wrote:

You can see an example in a recent posting:
http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/381414

But this can be achieved easier, as e.g. (0..9).cycle already returns an
Enumerator.

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