From: Daniel DeLorme <dan-ml@...42.com>
Date: 2008-02-07T11:17:08+09:00
Subject: string[0..-1] no longer uses copy on write

As the subject states, in 1.8 string[0..-1] used copy on write but in 
1.9 it does not, i.e.

$ ruby1.8 -ve 'x="x"*1000000; list=(0..99).map{ x[0..-1] }; system("ps u 
#{$$}")'
ruby 1.8.4 (2005-12-24) [i486-linux]
USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
dan42    27732  0.0  0.1   4052  2524 pts/25   S+   11:11   0:00 ruby1.8

$ ruby1.9 -ve 'x="x"*1000000; list=(0..99).map{ x[0..-1] }; system("ps u 
#{$$}")'
ruby 1.9.0 (2008-02-06 revision 0) [i686-linux]
USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
dan42    27736 42.0  5.0 103784 101552 pts/25  Sl+  11:11   0:00 ruby1.9

Should that be considered a bug?

On a related topic, why is copy on write not used for String#dup ?

Daniel