From: Robert Dober <robert.dober@...>
Date: 2006-06-27T01:38:56+09:00
Subject: Re: Ruby and Java equality usage

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On 6/26/06, Robert Klemme <shortcutter@googlemail.com> wrote:
>
> 2006/6/26, Robert Dober <robert.dober@gmail.com>:
> <SNIP>
>
> I don't fully agree to your point.  Basically =3D=3D and eql? are meant t=
o
> implement object equivalence.  So if you implement =3D=3D you should be
> implementing eql? and hash, too.  And usually =3D=3D and eql? should
> behave the same.  The page you mention quotes "For objects of class
> Object, eql? is synonymous with =3D=3D. Subclasses normally continue this
> tradition, but there are exceptions.". Numbers make a suble difference
> here:


Are you sure you read the page correctly?
I copy paste:

<begin doc>
 obj =3D=3D other =3D> true or false
obj.equal?(other) =3D> true or false
obj.eql?(other) =3D> true or false
 <http://www.ruby-doc.org/core/classes/Object.src/M001416.html>

Equality=97At the Object <http://www.ruby-doc.org/core/classes/Object.html>=
level,
=3D=3D returns true only if *obj* and *other* are the same object. Typicall=
y,
this method is overridden in descendent classes to provide class-specific
meaning.

Unlike =3D=3D, the equal? method should never be overridden by subclasses: =
it is
used to

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

determine object identity (that is, a.equal?(b) iff a is the same object as
b).

The eql? method returns true if *obj* and *anObject* have the same value.
Used by Hash <http://www.ruby-doc.org/core/classes/Hash.html> to test
members for equality. For objects of class
Object<http://www.ruby-doc.org/core/classes/Object.html>,
eql? is synonymous with =3D=3D. Subclasses normally continue this tradition=
, but
there are exceptions.
Numeric<http://www.ruby-doc.org/core/classes/Numeric.html>types, for

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

example, perform type conversion across =3D=3D, but not across eql?, so:

   1 =3D=3D 1.0     #=3D> true
   1.eql? 1.0   #=3D> false

<end doc>
Now unless this is wrong, one can conclude that
* #equal? shall not be redefined,
* #eql? should not be redefined, unless 1's knowing what one's doing (not 4
me ;=3D)
but
* #=3D=3D can be redefined freely.

>> 1 =3D=3D 1.0
> =3D> true
> >> 1.eql? 1.0
> =3D> false


Personally I find this situation a bit odd.  I'd prefer a single
> equivalence relation per class not two.


Although I do not feel the same that seems a normal concern, as I pointed
out to the OP.
Honestly I think it depends on the programming culture we are coming from
and when
in our mind these are synonyms we are likely to get bitten by that kind of
code.
I can only offer you my sympathy not my agreement.

But if we discuss this long enough it will become completely engraved in ou=
r
minds in we will be aware of it even if we do not like it ;)

Cheers
Robert

Kind regards
>
> robert
>
> --
> Have a look: http://www.flickr.com/photos/fussel-foto/
>
>

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