irb(main):001:0> class Welcome
irb(main):002:1>   def sostituto(nome = "a tutti")
irb(main):003:2>    nome = @nome
irb(main):004:2>   end
irb(main):005:1>   def buongiorno
irb(main):006:2>    puts "Buondì #{@nome}"
irb(main):007:2>   end
irb(main):008:1>   def buonanotte
irb(main):009:2>    puts "Arrivederci #{@nome}"
irb(main):010:2>   end
irb(main):011:1> end
=> nil
irb(main):012:0> p = Welcome.new("Claudio")
ArgumentError: wrong number of arguments (1 for 0)
    from (irb):12:in `initialize'
    from (irb):12:in `new'
    from (irb):12
    from :0