The Book of Ruby

Integers Are Special

In Ruby, an integer (or Fixnum) has a fixed identity. Every instance of the number 10 or every variable to which the value 10 is assigned will have the same object_id. The same cannot be said of other data types. Each instance of a floating-point number such as 10.5 or of a string such as “hello world” will be a different object with a unique object_id. Be aware that when you assign an integer to a variable, that variable will have the object_id of the integer itself. But when you assign some other type of data to a variable, a new object will be created even if the data itself is the same at each assignment:

object_ids.rb

# 10 and x after each assignment are the same object puts( 10.object_id ) x = 10 puts( x.object_id ) x ...