Inspired by http://www.justinweiss.com/blog/2014/11/24/each-dot-dot-dot-or-else/

gistfile1.rb

module Enumerable
  def each_with_emptiness
    return to_enum(__callee__) unless block_given?

    if empty?
      yield nil, true
    else
      each do |element|
        yield element, false
      end
    end
  end
end

[].each_with_emptiness do |n, empty|
  break puts "None found" if empty
  puts "Number: #{n}"
end

# >> None found

I like it, but I have a couple of questions (which may go beyond the original intention of the gist, in which case, sorry to bother you).

First off, I think this also begs for a .with_emptiness method on Enumerator, since all each_with_x methods I know of (which is, admittedly, only 2: each_with_object and each_with_index) are also available als each.with_x

And would it, then, help to implement this as something like this, or am I missing some subtleties (aside from the fact that this kind of methods on Enumerator is usually implemented in C)?

module Enumerable
  def each_with_emptiness(&block)
    each.with_emptiness(&block)
  end
end

class Enumerator
  def with_emptiness
    return to_enum(__callee__) unless block_given?

    begin
      peek

      each do |element|
        yield element, false
      end
    rescue StopIteration
      yield nil, true
    end
  end
end

[].each_with_emptiness do |n, empty|
  break puts "None found" if empty
  puts "Number: #{n}"
end

@ReneB I think the use of peek and StopIteration is a nice update as Enumerator does not require a #empty?