Question

I have an author class:

class Author < ActiveRecord::Base
  def to_s
    name
  end
end

Defining to_s allows me to do puts Author.first, but not puts Author.first.rjust(10):

NoMethodError: undefined method `rjust' for #<Author:0x21eb5d4>

Wouldn’t it be better if Ruby automatically tried to_s before the string method in cases like this? Is there any way to get this behavior?

Answer 1

First off, no, it wouldn’t. I don’t want ruby to just say “Hey, maybe this is a string method, let me see if I can run it after running to_s” on an arbitrary object. That being said, there are two solutions to what you want to do:

If you want to say “On any Author instance, if someone calls a method that it doesn’t have, but that String does, then it should magically call to_s“, then do this:

class Author < ActiveRecord::Base
  def to_s
    name
  end

  def method_missing(s, *a)
    x = to_s
    if x.respond_to? s then
      return x.send(s, *a)
    else
      super
    end
  end
end

If you want to say “rjust on anything that isn’t a String should mean calling to_s first”, then:

class Object
  def rjust(*a)
    to_s.rjust(*a)
  end
end

(Repeat with other methods as desired; note that this allows you to do things like 86.rjust(10); whether that’s a good thing or not may be a matter of taste)