From: Jean-Hugues ROBERT <jean_hugues_robert@...>
Date: 2004-04-23T21:20:56+09:00
Subject: Re: Creating bang methods

At 08:19 22/04/2004 +0900, you wrote:
>Hi --
>
>"Jon Hurst" <jon@jonathan.hurst.name> writes:
>
> > On reflection, perhaps I have not been clear enough. I would like to create
> > bang methods of some math functions (mostly abs), but I don't know how to
> > modify the reciever in place because the value of self cannot be changed.
> > It's not really important that I be able to write these bang methods, but I
> > would very much like to understand how one would do it.
> >
> > Class Numeric
> >     def abs!
> >         ??
> >     end
> > end
>
>Not being able to assign to self actually isn't the issue (no method
>can do that).  I think you want this:
>
>   x = -1
>   x.abs!
>
>to result in x == 1, but that isn't how bang methods work; i.e., they
>don't assign a new object to a variable, but rather they change an
>object in place (and, if there are one or more variables referencing
>that object, those variables don't "know" that this has happened).
>
>   irb(main):002:0> x = [1,2]
>   => [1, 2]
>   irb(main):003:0> x.id
>   => 537881530
>   irb(main):004:0> x.reverse!
>   => [2, 1]
>   irb(main):005:0> x.id
>   => 537881530
>
>Nothing has happened to x in this example (no reassignment) but the
>underlying array has been modified.
>
>The problem with abs! is that you can't modify a number in place,
>because numbers are immediate values (even when referenced by
>variables), and there's only one copy of each in existence.  So if you
>did this:
>
>   -1.abs!
>
>then henceforth 1 + -1 would be 2, because you would have changed -1
>*itself* to 1 (not just assigned 1 to a variable that previously
>referenced -1).  The same would be true of this:
>
>   x = -1
>   x.abs!   # x is the immediate value -1
>
>This is also why there are no ++ and -- operators in Ruby.  1++ would
>mean that the actual number 1 would henceforth mean 2.
>David

Well... something++ could get expanded into (something = something.++()) ?
And ++something get expanded into (tmp = something, something = 
something.++(), tmp)
Pure syntax sugar.
Then you can:
   def ++()
     self + 1
   end
I think += does that already, doesn't it ?
There are other reasons why there is no ++ in Ruby.

Jean-Hugues