Fixed Object Id for System Objects and Small Integers in Ruby

Question

Why do system objects like nil, true or false have a fixed object id in Ruby. Also I tried printing out the object ids of numbers, they are the same and follow an odd number sequence pattern. Any explanation for this?

[nil,true,false].each { |o| print o.object_id, ' '}
4 2 0 => [nil, true, false]

>> (0..50).each { |i| print i.object_id, ' ' }
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53 55 57 59 61 63 65 67 69 71 73 75 77 79 81 83 85 87 89 91 93 95 97 99 101 => 0..50

Answer 1

The following two links explain the concept behind Ruby's object IDs:

http://www.oreillynet.com/ruby/blog/2006/01/the_ruby_value_1.html http://www.oreillynet.com/ruby/blog/2006/02/ruby_values_and_object_ids.html

The object ID is calculated from the objects value plus some additional information. From that calculation you can derive the values you are seeing in your examples.