fib_solution.rb

# Each instance of FibSequence remembers how many Fibonacci numbers are
#   desired using the @limit instance variable.
# FibSequence#each is just  an instance method that yields the
#   first @limit Fibonacci numbers one at a time.
class FibSequence
  include Enumerable
  def initialize(limit) ; @limit = limit ; end
  def each
    case @limit
    when 0 then return
    when 1 then yield 1
    else
      yield 1
      yield 1
      lastfib,nextfib = 1,2
      @limit.downto(3) do
        yield nextfib
        lastfib, nextfib = nextfib, nextfib+lastfib
      end
    end
  end
end