meet it

Give your own class an `each`, and people can loop over it.

A playlist could be a plain array, but then any part of the program can reach in and mess it up. Professionals wrap the array in a class and keep it private. To let others , going through the items one by one, give the class an each method that yields every item.

Inside, each borrows the array's own each and passes each song on with yield. From outside, your playlist now behaves like any : road_trip.each do |song| reads the same as looping over an array, but nobody can touch @songs directly.

class Playlist
  def initialize(songs)
    @songs = songs
  end
  def each
    @songs.each { |song| yield song }
  end
end
road_trip = Playlist.new(["Africa", "Mr Blue Sky", "Toxic"])
road_trip.each do |song|
  puts "Now playing: #{song}"
end

Your each decides what callers see and in which order, because the block only runs when you yield.

guess first

This `each` is choosy. What will this show?

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

class Library
  def initialize(books)
    @books = books
  end
  def each
    @books.each do |title, on_loan|
      yield title if !on_loan
    end
  end
end
library = Library.new({ "Dune" => false, "Emma" => true, "Holes" => false })
library.each { |title| puts title }

your turn

Your turn. Let people loop over a recipe.

In the first blank, make each hand every ingredient to the caller's block. Add a fourth ingredient of your choice in the second blank.

Your code

press run to see what happens

fix it

Everyone is ready, but nobody has a name. Fix it.

Broken code to fix

press run to see what happens

Every line says is ready, but with no name. What does the caller's block receive?
yield on its own hands the block nothing, so player is nil inside it.
On line 6, change yield to yield player, then press run.

nailed it

your class can be looped over now. :D

Keep the array private and give the class an each.
each yields every item to the caller's block.
Your each decides which items callers see, and in what order.

new words in your collection

iterate
collection

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Give your own class an each, and people can loop over it.

This each is choosy. What will this show?

Your turn. Let people loop over a recipe.

Everyone is ready, but nobody has a name. Fix it.

your class can be looped over now. :D

Give your own class an `each`, and people can loop over it.

This `each` is choosy. What will this show?