From: Clemens Hintze <c.hintze@...>
Date: 1999-07-08T07:14:11+02:00
Subject: [ruby-talk:00434] Re: New feature for Ruby?


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On Thu, 08 Jul 1999, you wrote:
>Hi,
>
>This is not a comment for your code, sorry.  I will check it later. 
>
>In message "[ruby-talk:00431] Re: New feature for Ruby?"
>    on 99/07/07, Clemens Hintze <c.hintze@gmx.net> writes:
>

[...]

>You can replace the methods of existing class.  For exapmle,
>
>  class Integer
>    def succ(n=1)
>      ...
>    end
>    alias next succ
>    def pred(n=1)
>      ...
>    end
>    alias prev pred
>  end
>
>will do the job for you.  Oh, how dynamic Ruby is. :-)

:-00000

Woah! T h a t  i s  w o n d e r f u l !!! :-)))))))))))))))))

I didn't know, that this is possible... I did know concerning
Singleton methods... but this... <cannot believe what he sees...>

But does that mean, I cannot redefine an already defined class?
Means, if I want to totaly redefine the class e.g. Regexp. Perhaps
use another regexp engine, so nothing from the old class should
remain! As I have learned now, it is not enough to simply write

   class Regexp; ...; end

That would only enhanve/modify existant methods of already existant
class Regexp, true?

What I would have to do in that case? Not that I plan to do so. Only
I want to know :-)

BTW: I have attached Interval.rb again to that mail. This time with
classes Fixnum, Float and String modificated. Now the example looks
like it should. Only I would not define a String#pred in Ruby now.
Too lazy, sorry! :-)

Thanks again for that hint... and, of course, for that feature...
and, last but not least, for Ruby! :-)))))

>
>                                                matz.

\cle

PS: Would it makes sense to introduce that feature in the
Ruby-Manual? Perhaps it is, but I cannot remember I did see that!
Furthermore please explain `alias' more a little bit. I could not see
from the manual, whether the syntax is `alias old new' or `alias new
old'.
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#!/bin/env ruby


def interval(start, stop, step=3D1)
=09Interval::new(start, stop, step)
end


class Interval
=09include Enumerable

=09attr_reader :first, :last, :step

=09def initialize(start, stop, step=3D1)
=09=09raise ArgumentError, "XXX1" if not (start.respond_to?(:<=3D>))
=09=09up =3D ((start <=3D> stop) <=3D 0)=20
=09=09@cmp =3D up ? (:<=3D) : (:>=3D)
=09=09@advfn =3D up ? (:succ) : (:pred)
=09=09raise ArgumentError, "XXX2" if not (start.respond_to?(@advfn))
=09=09raise ArgumentError, "XXX3" if step <=3D 0
=09=09@first =3D start
=09=09@last =3D stop
=09=09@step =3D step
=09end

=09def each
=09=09value =3D @first
=09=09while (cmp =3D (value <=3D> @last)).send(@cmp, 0)
=09=09=09yield value
=09=09=09break if cmp =3D=3D 0
=09=09=09value =3D value.send(@advfn, @step)
=09=09end
=09=09nil
=09end

=09def [](index)
=09=09i =3D 0
=09=09each do |element|
=09=09=09return element if i =3D=3D index
=09=09=09i +=3D 1
=09=09end
=09=09nil
=09end
end


if __FILE__ =3D=3D $0

=09# As I have learned now, that with that sample syntax, I can
=09# override already defined methods, we can at once "improve" class
=09# Fixnum, Float and String to show, how it would works together
=09# with Interval

=09class Fixnum
=09=09def succ(n=3D1)
=09=09=09self + n
=09=09end
=09=09def pred(n=3D1)
=09=09=09self - n
=09=09end
=09end
=09=09=09
=09class Float
=09=09def succ(n=3D1)
=09=09=09self + n
=09=09end
=09=09def pred(n=3D1)
=09=09=09self - n
=09=09end
=09end

=09class String
=09=09alias oldsucc succ
=09=09def succ(n=3D1)
=09=09=09s =3D self
=09=09=09for i in 1..n
=09=09=09=09s =3D s.oldsucc
=09=09=09end
=09=09=09s
=09=09end
=09end

=09# Here begin the examples.

=09print "=3D=3D=3DUpwards Interval \"a\" .. \"e\"=3D=3D=3D\n"
    for i in interval("a", "e")
=09=09p(i)
=09end

=09print "=3D=3D=3DDownwards Interval 9 .. 1=3D=3D=3D\n"
=09for i in interval(9, 1)
=09=09p(i)
=09end

=09print "=3D=3D=3DUpwards 1.0 .. 9.0 step 1.25=3D=3D=3D\n"
=09for i in interval(1.0, 9.0, 1.25)
=09=09p(i)
=09end

=09print "=3D=3D=3DDownwards 9 .. 1 step 3=3D=3D=3D\n"
=09i =3D Interval::new(9, 1, 3)
=09i.each{ |el| p(el) }

=09print "=3D=3D=3DIs 3 in that interval? (answer: true): "
=09p(i.include?(3))

=09print "=3D=3D=3DIs 2 in that interval? (answer: false): "
=09p(i.include?(2))

=09print "=3D=3D=3DWhat is the first element? (answer: 9): "; p(i[0])
=09print "=3D=3D=3DWhat is the second element? (answer: 6): "; p(i[1])
=09print "=3D=3D=3DWhat is the third element? (answer: 3): "; p(i[2])
end

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