According to "The Well Grounded Rubyist" 2nd edition the following 
should increment the size of the all_symbols array by 2 for variables a 
and b but it doesn't:

>> Symbol.all_symbols.size
=> 3812
>> a = 1
=> 1
>> Symbol.all_symbols.size
=> 3812
>> b = 2
=> 2
>> Symbol.all_symbols.size
=> 3812
>> Symbol.all_symbols.include? :a
=> true
>> Symbol.all_symbols.include? :b
=> true
>> Symbol.all_symbols.size
=> 3812

I'm running Ruby version 2.1.0 on Mac OS X.

gvim