require "virtus"

class Address
  include Virtus.model

  attribute :street, String
  attribute :city, String
end

class User
  include Virtus.model

  attribute :name, String
  attribute :address, Address, default: Address.new
end

# 2.3.1 (main):0 > User.new(name: "joe")
# => #<User:0x0000000255ed60 @address=#<Address:0x0000000255ec70 @city=nil, @street=nil>, @name="joe">
# 2.3.1 (main):0 > User.new(name: "joe", address: nil)
# => #<User:0x000000024ccd20 @address=nil, @name="joe">
# 2.3.1 (main):0 > User.new(name: "joe", address: {})
# => #<User:0x00000002463d48 @address=#<Address:0x00000002463c80 @city=nil, @street=nil>, @name="joe">