Re: String#upto edge case - empty string causes infinite loop

On 1/9/07, Berger, Daniel <[e-mail]> wrote:
> > -----Original Message-----
> > From: Arnaud Bergeron [mailto:[e-mail]]
> > Sent: Tuesday, January 09, 2007 1:36 PM
> > To: [e-mail]
> > Subject: Re: String#upto edge case - empty string causes infinite loop
> >
> >
> > On 1/8/07, Berger, Daniel <[e-mail]> wrote:
> > > > -----Original Message-----
> > > > From: Arnaud Bergeron [mailto:[e-mail]]
> > > > Sent: Monday, January 08, 2007 12:49 PM
> > > > To: [e-mail]
> > > > Subject: Re: String#upto edge case - empty string causes infinite
> > > > loop
> > >
> > > <snip>
> > >
> > > > Since "\377".succ yields "\001\000" I belive it would make more
> > > > sense having "".succ return "\000" and continue on from there.
> > >
> > > Hm, it does seem to be a tradition among other languages:
> >
> > These examples are not exactly the same situation, as none of
> > these languages have the equivalent of succ for strings.
> >
> > > # Perl
> > > my $str = "";
> > > print ++$str; # 1
> >
> > Perl is the only language I'm not familiar with here, so I am
> > not really sure what happens here but I heard about automagic
> > conversion of string to numbers.
> >
> > > /* C */
> > > #include <stdio.h>
> > >
> > > int main(){
> > >    char* empty = "";
> > >    printf("Value: %i\n", atoi(empty) + 1); /* 1 */
> > >    return 0;
> > > }
> >
> > Here you are explicitly converting the string to a number
> > (and due to stupidity, atoi interprets "" as being the number
> > 0).  After adding 1 it is no suprise that it prints 1.
>
> Well, I guess my point was that atoi("") returns 0, stupid or not.
>
> > > /* Java */
> > > public class EmptyTest{
> > >    public static void main(String[] args){
> > >       String empty = "";
> > >       System.out.println(empty + 1); /* 1 */
> > >    }
> > > }
> >
> > Here you get string concatenation.  You could have written ""
> > + "1" and it would have only been more explicit.  The number
> > 1 gets converted to a string and if you concatenate that
> > string with the empty string you get "1".
>
> Oops, right.
>
> > The .succ function is a different beast than these examples
> > because it returns the next string in order.
> >
> > > > However there might be a problem because letters are treated
> > > > differently.  "z".succ yield "aa" and not "}" and the
> > same is true
> > > > for "Z" so this might need more thought, but in my
> > opinion yielding
> > > > the empty string once is the last expected behavior.
> > >
> > > As you suggest, I'm not sure what repurcussions changing the return
> > > value of "".succ might have.  My approach at least has the
> > advantage
> > > of being safe in that regard.  However, I can live with either
> > > approach. It is just an edge case after all. :)
> >
> > I would have it return "\000" because "" < "\000" and is the
> > lowest value for a string for which this inegality is true.
> > Having "".succ return "" breaks the implicit assuption that
> > foo < foo.succ.
> >
> > irb(main):001:0> a = 1
> > => 1
> > irb(main):002:0> a < a.succ
> > => true
> > irb(main):003:0> a = ""
> > => ""
> > irb(main):004:0> a < a.succ
> > => false
>
> I understand your point, but I could just as well argue that there is no
> logical successor to an empty string, and therefore it's a special case.
> Another point to consider is that, if we have "".succ return "0", we get
> this result from String#upto:

I think you missunderstood something.  I don't propose it returns "0"
but "\000" which the character with ASCII value 0 (i.e. NUL).  I agree
it could be some other value, but why I chose this one is because that
is the string with the "smallest" (as determined by <) value which is
bigger than "".

> "".upto(2) => ["", "0", "1", "2"]
>
> Either approach feels more or less arbitrary. I vote to err on the side
> of caution and stick with my original patch. :)

I think this issue might not be as important as I let it show because
this is not common code.  I still feel that ("" < "".succ) == false is
wrong though.

However, if succ is not going to change, then it's better to have your
patch than nothing.

Last but not the least.  I realize I have not provided a patch for my
solution.  Well here it is:

--- string.c.orig	Wed Jan 10 22:52:14 2007
+++ string.c	Wed Jan 10 23:18:12 2007
@@ -1392,7 +1392,6 @@

     str = rb_str_new5(orig, RSTRING(orig)->ptr, RSTRING(orig)->len);
     OBJ_INFECT(str, orig);
-    if (RSTRING(str)->len == 0) return str;

     sbeg = RSTRING(str)->ptr; s = sbeg + RSTRING(str)->len - 1;



> Regards,
>
> Dan
>
>
> This communication is the property of Qwest and may contain confidential or
> privileged information. Unauthorized use of this communication is strictly
> prohibited and may be unlawful.  If you have received this communication
> in error, please immediately notify the sender by reply e-mail and destroy
> all copies of the communication and any attachments.
>
>


-- 
I'm trying to launch the internet; so I open a terminal and go
"percent sign 'Internet'" at the prompt and it doesn't work. What
gives??!! -- random troll