When Enumerable is included, the class must provide “each” method.

We have to be careful not to forget it.

When I was writing codes like below referring to a book, I noticed the fact that each method is not used but included.

class Comics
  extend Forwardable
  def_delegators :@comics, :size, :each
  include Enumerable

  def initialize(comics)
    @comics = comics
  end
  def publishings
    @comics.select{ |comic| comic.published }
  end
end

If each is not included, the codes output an error like this in publishing method.

undefined method `each' for #<Comics:0x00007fde00873030> (NoMethodError)

That was confusing because each method was not defined in Comics class.

However, checking out ruby-doc helped me to understand the cause.

Enumerable

“The class must provide a method each, which yields successive members of the collection.”

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