Ruby

A little ObjectSpace exploration gives:

n = 1 GC.disable a = ObjectSpace.count_objects[:T_STRING] strings = {} ObjectSpace.each_object(String) { |s| strings[s.object_id] = s } n.times { ENV["HOME"] } b = ObjectSpace.count_objects[:T_STRING] p a => b p (b-a)/n.to_f new_strings = ObjectSpace.each_object(String).reject {|s| strings.key? s.object_id } p new_strings p new_strings.size 

ObjectSpace.count_objects seems unreliable in this case, sometimes the number of T_STRING is less after invocations of ENV["HOME"] yet the GC is supposed to be disabled.

The difference using ObjectSpace.each_object give us the 3 String:

["/home/me", "UTF-8", "HOME"] 

I am a bit concerned about the "UTF-8" String created.
"HOME" is created each time, and could be avoided by assigning it to a variable.
After all, the compiler is not supposed to know ENV[] is not modifying its argument,
and there is no clue the String should be immutable.
(detection of literal .freeze should help, but will anyone do ENV["HOME".freeze] ?
Anyway real code would likely not invoke ENV[var] many times for the same var)