Example of `yield self`

first.rb

class Pokemon
  def battle
    yield self
  end
end

mewtwo = Pokemon.new

mewtwo.battle do |m2|
  puts m2
  puts m2.class
end

# => #<Pokemon:0x007f8b74080f28>
# => Pokemon

second.rb

class Pokemon
  def initialize(move)
    @move = move
  end

  def battle
    yield self
  end

  def use_move
    puts "used #{@move}!"
  end
end

mewtwo = Pokemon.new "Psychic"

mewtwo.battle do |m2|
  m2.use_move
end

# => used Psychic!

arceus = Pokemon.new "Judgement"

arceus.battle do |arc|
  arc.use_move
end

# => used Judgement!