What is the object in Ruby's "hello world"?

Question

If everything is an object in Ruby, to the point that even math operators are methods applied to objects, when I write:

puts "Hello world"

The method is puts, and the parameter is "Hello world", but what is the object?

Answer 1

puts

To find a method, you could call :

method(:puts)
#=> #<Method: Object(Kernel)#puts>

So puts is a method defined in Kernel, available to every Object.

Kernel#puts

puts "Hello world"

is actually

self.puts( String.new("Hello world") )

Where self is the object main.

So puts "hello world" is a :

• Kernel#puts method call
• on main
• with a String object as argument.

Notes

Note that if you execute

self.puts( String.new("Hello world") )

you'll get an error :

private method `puts' called for main:Object (NoMethodError)

Because every Kernel method is made available to every Object, but as a private method. You'd need :

self.send(:puts, String.new("Hello world") )

Test

Another way to check would be :

module Kernel
  def my_puts(*args)
    print "Calling Kernel#my_puts on #{self} with #{args}\n"
    print "Now delegating to Kernel#puts on #{self} with #{args} :\n"
    puts(*args)
  end
end

my_puts "Hello world"

It outputs :

Calling Kernel#my_puts on main with ["Hello world"]
Now delegating to Kernel#puts on main with ["Hello world"] :
Hello world

See? Everything is an object, even though it might not look like it.

2+3

In the same vein : 2+3 is actually Integer(2).+( Integer(3) ).