calling object's method in method definition in Ruby

gistfile1.rb

irb(main):001:0> class Foo
irb(main):002:1>   def initialize(a, b = a.to_s)
irb(main):003:2>     puts [a, b].inspect
irb(main):004:2>   end
irb(main):005:1> end
=> nil
irb(main):006:0> Foo.new 1
[1, "1"]
=> #<Foo:0x007f973d9ca410>