Question

class A
  def initialize(string, number)
    @string = string
    @number = number
  end

  def to_s
    "In to_s:\n   #{@string}, #{@number}\n"
  end
  def to_a
    "In to_a:\n   #{@string}, #{@number}\n"
  end
end
puts a = A.new("hello world", 5)

output is

 In to_s:
   hello world, 5

How is the to_s method called automatically?

Why isn’t another method called automatically such as to_a?

Since I did not write puts in the to_s method, why is output printed.

Answer 1

You’re sending it to puts, which will try to render the object as a string using to_s.

If you changed your last line to: puts A.new("hello world", 5).to_a, it would instead call to_s on the returned Array and A’s to_s would not be called.