From: 7stud -- <bbxx789_05ss@...>
Date: 2011-04-10T03:18:03+09:00
Subject: Re: Calling to_enum on a MatchData object

Vahagn Hayrapetyan wrote in post #991914:
> Thank you for your explanations, I can see now that :each is an
> inherited method and it had to be ferreted out of the MatchData set of
> methods.
>

I'm not sure what you are referring to because each() is neither defined 
nor inherited in the MatchData class.  Check the output of:

md = /h/.match('hello')
puts md.methods.sort

And Enumerator defines its own each() method.


> So in order to use an enumerator, an object itself has to define an
> (:each) method and then an enumerator just augments that.

No.  An enumerator can be hooked up to any "iteration method" for an 
object.  An "iteration method" is any method that calls yield().  Here 
is an example:

class Dog
  def bark
    yield 'woof'
    yield 'whooooo'
    yield 'ruuuff'
  end
end

dog = Dog.new
e = dog.enum_for(:bark)

results = e.select{|sound| sound[0] == 'w'}
p results

--output:---
["woof", "whooooo"]


results = e.map{|sound| "#{sound.capitalize}!}" }
p results

--output:--
["Woof!}", "Whooooo!}", "Ruuuff!}"]


if e.include?('woof')
  puts 'yes'
end

--output:--
yes


You may be confusing Enumer-ator with something you read about 
Enumer-able.  If you want to make the Enumer-able methods available to 
your class, e.g. group_by(), each_slice(), select(), map(), include?(), 
etc., then your class has to:

1) Define an each() method, and
2) include Enumerable

Now the confusing part: the Enumer-ator class defines a few of its own 
methods, but it also includes Enumer-able, so an enumerator object has 
both the Enumerator and Enumerable methods available to it.

An enumerator can also be hooked up to a block that you define:

e = Enumerator.new do |y|
  10.upto(14) do |num|
    y << num
  end
end

results = e.map{|x| x + 5}
p results

--output:--
[15, 16, 17, 18, 19]

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