[ruby-talk:00416] Re: New feature for Ruby?

On Thu, 01 Jul 1999, Yukihiro Matsumoto wrote:
>Hi Clemens,
>
>In message "[ruby-talk:00407] New feature for Ruby?"
>    on 99/07/01, [e-mail] <[e-mail]> writes:
>
>|So here are my ideas:
>
>In summary, your proposal should be:
>
>  (a) make Range be able to iterate reverse order if beg > end.
>
>  (b) make step can be supplied to Range::new.
>
>  (c) add Range#[n] to retrieve n-th item of the iteration.
>
>  (d) make String's magic decrement possible (as magic increment).
>
>Right?  My ideas for the proposal are:

That's right. I know I could count on you to simplify and make clear
my proposal :-)))

But your have forgot one:

(e) allow to give the "succ" method (and the corresponding "pred"
    one) a stepsize as optional argument.

>
>  (a) Range is range, not interval;  I think you'd better define
>      Interval class to do the work.

Ahem... <think>, <think>, <think>... Ok! I can understand your
reasons. But if so, do you think, it would be useful, to have a
build-in syntax for creating an Interval? I very like it to have
(a..b).each{...}. But I don't know, whether it is necessary or not.

But thinking more and more about it, I think it would be better to
have an Interval class and let the Range class be untouched!

>
>  (b) Ditto.  There may be the possibility of Range#step.

Ok!

>
>  (c) I'm not sure;  I'd like to hear others' opinion.

I think, if you mean we should have Interval instead of Range, I
don't think, it would be necessary to have the "[]" method. :-)

>
>  (d) It's good.  The only reason for absence of String's magic
>      increment is my laziness.  I'm happy to add magic decrement
>      feature to the String class, if somebody supplies me the code
>      (acutually you already did).

But please consider, that "a".pred currently results in "". Whereas
"".succ and "".pred cause errors. I don't know, if that implemented
behavior is ok, or not. But, nevertheless, please feel free to use it
:-)))

>
>And your proposal
>
>|Every class which wants to be used as Range, should implement a
>|"succ", "pred" and a "compare method" to enable us to detect the end
>|of iteration.
>
>is already there, except "pred" and reverse ordering.

No! As I have already mentioned, the current implementation lacks of
the optional stepsize argument. I think, that is important. Because
only an instance itself nows, how to return the n'th successor.
Furthermore it would be more fast than calling the "succ" method n
times!

>
>Concerning Interval, I'm affraid it should be restricted to the numric
>intervals.  For example, by String's magic increment, "a000" never
>reaches "bcde", even though latter is larger lexicographically.  It
>may raise the problem sometimes.  But with numerical values, Intervals
>are much easier to operate.

Oops! That I have never thought about! But... waitamomentplease...
<klickedi> <klackedi> ... :-)))))

The same is true for current Range instances. "a000".."bcde" would
also not behave as expected... :-P

Furthermore I really would not like to restrict it only to numeric
arguments. Later I will implement a new class perhaps, which usage as
interval could also make sense. So I would like to let the user
decide, what class should be used by an Interval. The only
requirement would be, that this class have to implement a "succ",
"pred" and "cmp" method!

>
>                                                matz.

Thanks for all of your thoughts. I think I will implement an Interval
class instead of changing the existant Range class. But I would
really need the "succ" and "pred" methods WITH optional stepsize
argument. Could we patch these methods to my needs?

Cle.