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.

> /* 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".

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


> Regards,
>
> Dan
>
>
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