static-types-and-type-checking-in-ruby-3-0.rb

# a Person type declared in sig/person.rbs
class Person
  @name: String
  @contacts: Array[Email]

  def initialize: (name: String) -> untyped
  def name: -> String
  def contacts: -> Array[Email]
end

# an Email type declared in sig/email.rbs (and referenced on lines 4 and 8 above)
class Email
  @address: String

  def initialize: (address: String) -> untyped
  def address: -> String
end