module Kernel
end

module Gem
  class Specification
    attr_reader version (): Version

    attr_reader gem_dir (): String

    def self.find_by_name: (String name, ?String? version) -> instance
  end
end

class OptionParser
  def initialize: () ?{ (instance) -> void } -> void

  def on: [T] (*String) { (T) -> void } -> void

  attr_accessor version: String

  attr_accessor banner: String

  def order!: (Array[String]) -> void

  def parse!: (Array[String]) -> void

  def ver: () -> String

  def help: () -> String
end

module Enumerable[unchecked out Elem]
  def flat_map: [U] () { (Elem) -> Array[U] } -> Array[U]
              | [U] () { (Elem) -> U } -> Array[U]
              | ...
end