prelude: |
  h1, h10, h100, h1000 = [1, 10, 100, 1000].map do |n|
    h = {kw: 1}
    n.times{|i| h[i.to_s.to_sym] = i}
    h
  end
  eh = {}
  def kw(kw: nil, **kws) end
benchmark:
  1: |
    kw(**h1)
  1_mutable: |
    kw(**eh, **h1)
  10: |
    kw(**h10)
  10_mutable: |
    kw(**eh, **h10)
  100: |
    kw(**h100)
  100_mutable: |
    kw(**eh, **h100)
  1000: |
    kw(**h1000)
  1000_mutable: |
    kw(**eh, **h1000)