meet it

With no block, `each` should hand back an .

Call an array's each with no block and you get an enumerator: an object that remembers its place, like a bookmark. Ask it for .next and it hands out one item, then waits. Or chain it, as in each.with_index(1), to add a counter that starts at 1.

Your own each should behave the same way. Start it with and Ruby builds the enumerator for you. When next runs out of items it raises , and loop do treats that as a polite signal to stop.

class Playlist
  def initialize(songs)
    @songs = songs
  end
  def each
    return to_enum(:each) unless block_given?
    @songs.each { |song| yield song }
  end
end
songs = Playlist.new(["Africa", "Mr Blue Sky", "Toxic"])
player = songs.each
puts player.next
puts player.next
songs.each.with_index(1) { |song, place| puts "#{place}. #{song}" }

unless is Ruby's if not, and loop do ... end repeats its block until something stops it.

guess first

The queue runs dry. What will this show?

Guess before you run it. Wrong guesses are how you learn, and nothing is marked.

queue = ["Ana", "Ben", "Cy"].each
loop do
  puts "Serving #{queue.next}"
end
puts "Queue empty"

your turn

Your turn. Number the steps of a recipe.

Make each return an enumerator when there is no block, add a last step of your own, then make the numbering start at 1.

Your code

press run to see what happens

fix it

The leaderboard cannot number its players. Fix `each`.

Broken code to fix

press run to see what happens

board.each is called with no block. What does yield do when there is no block?
With no block, each should hand back an enumerator instead of yielding.
Add return to_enum(:each) unless block_given? as the first line inside each.

nailed it

you made enumerators hand out items. :D

With no block, each should return to_enum(:each).
next hands out one item and raises StopIteration at the end.
with_index(1) numbers items starting from 1.

new words in your collection

enumerator
to_enum
StopIteration

This lesson isn’t saved. A free account remembers every lesson you finish.

With no block, each should hand back an enumerator.

The queue runs dry. What will this show?

Your turn. Number the steps of a recipe.

The leaderboard cannot number its players. Fix each.

you made enumerators hand out items. :D

With no block, `each` should hand back an .

The leaderboard cannot number its players. Fix `each`.