Ruby block_given?

def arithmetic_sequence(init: 1, diff: 1, count: 10)
  current = init
  if block_given?
    count.times do
      yield(current)
      current += diff
    end
  else

    # tapメソッドのブロックではArray.newに対して設定する
    Array.new.tap do |a|
      count.times do
        a << current
        current += diff
      end
    end
  end
end

# blockが渡された場合
arithmetic_sequence(init: 2, diff: 3, count: 5) do |n|
  puts n
end

=begin
結果 => 2
5
8
11
14
=end

# block渡されていない場合
p arithmetic_sequence(init: 2, diff: 3, count: 5)

# 結果 => [2, 5, 8, 11, 14]