Hi,

At Tue, 17 Dec 2002 03:40:37 +0900,
Matt Armstrong wrote:
> Actually I think the "elegant" solution to the problem is lazy string
> copies.  E.g.
> 
>     s2 = s1[50..-1] # Does not actually copy data until s1 (or s2)
>                     # is modified.  s1 and s2 must know they share
>                     # data.
>     s2 =~ /\Afoo/
> 
> I remember mention of some work being done on this, but there were
> implementation problems.

A String instance always has '\0' terminator not included in
its length.  So tried just tail sharing.


Index: string.c =================================================================== RCS file: /cvs/ruby/src/ruby/string.c,v retrieving revision 1.125 diff -u -2 -p -r1.125 string.c --- string.c 10 Dec 2002 06:23:40 -0000 1.125 +++ string.c 16 Dec 2002 22:54:13 -0000 @@ -475,6 +475,16 @@ rb_str_substr(str, beg, len) if (len == 0) return rb_str_new5(str,0,0); - str2 = rb_str_new5(str,RSTRING(str)->ptr+beg, len); - OBJ_INFECT(str2, str); + if (len > sizeof(struct RString)/2 && + beg + len == RSTRING(str)->len && + !FL_TEST(str, STR_ASSOC)) { + if (!FL_TEST(str, ELTS_SHARED)) str = rb_str_new4(str); + str2 = rb_str_new3(str); + RSTRING(str2)->ptr += beg; + RSTRING(str2)->len = len; + } + else { + str2 = rb_str_new5(str,RSTRING(str)->ptr+beg, len); + OBJ_INFECT(str2, str); + } return str2;
-- Nobu Nakada