cases.rb

module Kernel
  def cases(o, cases={})
    o = [o] unless o.is_a? Array
    raise "invalid" unless o[0].is_a? Keyword

    selection = cases[o[0]] || cases[:else] || raise("non-exhaustive cases!")
    selection.call(*cases[1..-1])
  end
end

order = [:delivery, "123 Main St."]
order = [:digital, "customer@example.com"]
order = [:pickup, 456]

cases(order,
  delivery: ->(addr) { ... }
  digital: ->(email) { ... }
  pickup: ->(store_id) { ... }
)