From: ts <decoux@...>
Date: 2000-12-08T22:24:21+09:00
Subject: [ruby-talk:6937] Re: Some performance issues

>>>>> "B" == Ben Tilly <ben_tilly@hotmail.com> writes:

B> OK, this has me curious.  How was this done internally?

 When ruby compile a script and find $&, $', ... it will create a node
 BACK_REF (node NTH_REF for $1, $2, ...) 

 When this node is executed, it retrieve the information stored in the
 variable $~ (which contain the string used for the regexp (stored via
 rb_str_new4()), and registers) and extract the part of the string
 corresponding to $&, ... 

 $~ (like $_) make reference to a local (and thread based) variable,
 i.e. when ruby call a def the first 2 local variables are $_ and $~

B> for it.  So it looks like it is lazy.  But when I try to
B> modify the string before having to work out $` and $' I
B> am unable to find a way to mess up $' and $`.  (Which is

 When ruby want to modify a string, it first verify if this string is
 associated with another string (like in the regexp case) and if this is
 true it make first a copy of the string before modifying it (see
 rb_str_modify() and rb_str_independent() in string.c).


Guy Decoux