Ruby Programming/Reference/Predefined Classes

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In ruby even the base types (also predefined classes) can be hacked.[1] In the following example, 5 is an immediate,[2] a literal, an object, and an instance of Fixnum.

class Fixnum

	alias other_s to_s
	def to_s()
		a = self + 5
		return a.other_s


a = 5
puts a.class  ## prints Fixnum
puts a        ## prints 10 (adds 5 once)
puts 0        ## prints 5  (adds 5 once)
puts 5        ## prints 10 (adds 5 once)
puts 10 + 0   ## prints 15 (adds 5 once)

b = 5+5
puts b        ## puts 15 (adds 5 once)

Footnotes[edit | edit source]

  1. ^ Which means the 4 VALUE bytes are not a reference but the value itself. All 5 have the same object id (which could also be achieved in other ways).
  2. ^ Might not always work as you would like, the base types don't have a constructor (def initialize), and can't have singleton methods. There are some other minor exceptions.