dpmethod.rb

class Hash
  def iloc(i, *rest, set: nil)
    if rest.empty?
      self[i] = set if set
      self[i]
    else
      self[i] = Hash.new if not self[i]
      self[i].iloc(*rest, set: set)
    end
  end
end

class DPMethod
  def initialize(f)
    @f = f
    @h = Hash.new
  end

  def call(*args)
    v = @h.iloc(*args)
    if not v
      v = @f.call(self, *args)
      @h.iloc(*args, set: v)
    end
    v
  end
end

=begin
fdp = DPMethod.new(->(fdp, i){
  case i
  when 0 then 0
  when 1 then 1
  else fdp.call(i - 2) + fdp.call(i - 1)
  end
})

fdp.call 30  # => 832040
=end