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Re: Objects comparaison ?

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dhtml wrote:

> Thomas 'PointedEars' Lahn wrote:
>> dhtml wrote:
>> > Thomas 'PointedEars' Lahn wrote:
>> >> Jukka K. Korpela wrote:
>> >> > 13.10.2011 22:21, Thomas 'PointedEars' Lahn wrote:
>> >> >> Java's equals() method [– which exists precisely for that purpose –
>> >> >> should provide a good start for an implementation in ECMAScript.]
>> >
>> > Java `Object.equals` does nothing more than use Java's == which is
>> > analagous to JavaScript's ===.
>>
>> I did not write `Object.equals()', if you cared to notice.
>
> Which Java equals() method did you mean?

Context matters.  By "should provide a good *start* for an implementation 
*in* ECMAScript" I was referring to the *concept* of Java's Object.equals() 
method, a method which is *overriden* by subclasses.

The OP was wondering about the difference between comparing two object 
references and two primitive strings in an ECMAScript implementation.  
Consider then, for example, String.equals(), which is necessary in Java 
because *there* *are* *no* *primitive* *string* *values* *in* *Java*, and
`x == "foo"' would be useless (it would always result in `false').  So you 
need to do x.equals("foo") or – better¹ – "foo".equals(x) in Java [1] for 
what you need only `==' in ECMAScript.

So comparing strings, for example, is more complicated in Java.  But by 
comparison ECMAScript's approach also is less powerful and less flexible 
because the way the comparison is performed there is more or less written in 
stone, defined by the algorithms in the Specification.

The concept of an equals() method, on the other hand, carries with it the 
necessity and the *possibility* for the software developer of defining what 
makes objects (of different types) equal, i. e. *which* field/property 
values of objects are compared against each other and what defines *their* 
(in)equality, which is what Jukka Korpela pointed out.

There are also other programming languages which implement this concept and 
similar ones; more recently Python, where the algorithm for the `==', `<', 
and `>' operations between objects can be defined by a __cmp__() method of 
the class of either object [2].

This concept can be implemented in an ECMAScript implementation, like 
JavaScript, as well; but, without sacrificing efficiency in existing 
implementations, [AFAIK] only in a Java-like way, so without the pythonic 
sugar.


HTH

PointedEars
___________
¹  IMHO "better" because we know that "foo" will evaluate to a new String
   instance in Java but we do not know about `x'.

[1] 
<http://download.oracle.com/javase/7/docs/api/java/lang/String.html#equals(java.lang.Object)>
[2] <http://docs.python.org/release/2.5.2/ref/customization.html>
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a Web page appears to be yearning for the bad old days, before the Web,
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Thread

Objects comparaison ? unbewusst.sein@fai.invalid (Une Bévue) - 2011-10-13 20:20 +0200
  Re: Objects comparaison ? "Jukka K. Korpela" <jkorpela@cs.tut.fi> - 2011-10-13 21:47 +0300
    Re: Objects comparaison ? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-10-13 21:21 +0200
      Re: Objects comparaison ? "Jukka K. Korpela" <jkorpela@cs.tut.fi> - 2011-10-13 22:40 +0300
        Re: Objects comparaison ? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-10-13 21:46 +0200
          Re: Objects comparaison ? dhtml <dhtmlkitchen@gmail.com> - 2011-10-13 13:11 -0700
            Re: Objects comparaison ? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-10-14 01:26 +0200
              Re: Objects comparaison ? dhtml <dhtmlkitchen@gmail.com> - 2011-10-14 12:41 -0700
                Re: Objects comparaison ? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-10-15 21:37 +0200
                Re: Objects comparaison ? Antony Scriven <adscriven@gmail.com> - 2011-10-15 15:51 -0700
                Re: Objects comparaison ? dhtml <dhtmlkitchen@gmail.com> - 2011-10-15 21:28 -0700
                Re: Objects comparaison ? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-10-16 11:41 +0200
                Re: Objects comparaison ? dhtml <dhtmlkitchen@gmail.com> - 2011-10-16 09:05 -0700
                Re: Objects comparaison ? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-10-16 21:59 +0200
                Re: Objects comparaison ? John G Harris <john@nospam.demon.co.uk> - 2011-10-17 10:53 +0100
                Re: Objects comparaison ? "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2011-10-17 07:02 -0700
                Re: Objects comparaison ? Andreas Bergmaier <andber93@web.de> - 2011-10-17 16:27 +0200
                Re: Objects comparaison ? dhtml <dhtmlkitchen@gmail.com> - 2011-10-17 21:28 -0700
                Re: Objects comparaison ? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-10-18 11:12 +0200
                Re: Objects comparaison ? John G Harris <john@nospam.demon.co.uk> - 2011-10-18 15:23 +0100
                Re: Objects comparaison ? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-10-18 19:48 +0200
                Re: Objects comparaison ? John G Harris <john@nospam.demon.co.uk> - 2011-10-19 17:08 +0100
                Re: Objects comparaison ? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-10-20 23:58 +0200
                Re: Objects comparaison ? Antony Scriven <adscriven@gmail.com> - 2011-10-20 15:46 -0700
                Re: Objects comparaison ? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-10-18 10:55 +0200
                Re: Objects comparaison ? John G Harris <john@nospam.demon.co.uk> - 2011-10-18 15:59 +0100
                Re: Objects comparaison ? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-10-18 19:33 +0200
                Re: Objects comparaison ? Scott Sauyet <scott.sauyet@gmail.com> - 2011-10-18 14:05 -0700
                Re: Objects comparaison ? "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2011-10-18 16:51 -0700
                Re: Objects comparaison ? "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2011-10-18 17:21 -0700
                Re: Objects comparaison ? Scott Sauyet <scott.sauyet@gmail.com> - 2011-10-19 04:40 -0700
                Re: Objects comparaison ? "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2011-10-19 16:41 -0700
                Re: Objects comparaison ? Antony Scriven <adscriven@gmail.com> - 2011-10-19 17:14 -0700
                Re: Objects comparaison ? "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2011-10-19 18:33 -0700
                Re: Objects comparaison ? Scott Sauyet <scott.sauyet@gmail.com> - 2011-10-23 11:43 -0700
                Re: Objects comparaison ? Antony Scriven <adscriven@gmail.com> - 2011-10-19 15:32 -0700
                Re: Objects comparaison ? "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2011-10-19 16:54 -0700
                Re: Objects comparaison ? Antony Scriven <adscriven@gmail.com> - 2011-10-19 17:32 -0700
                Re: Objects comparaison ? "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2011-10-19 18:39 -0700
                Re: Objects comparaison ? John G Harris <john@nospam.demon.co.uk> - 2011-10-19 16:32 +0100
                Re: Objects comparaison ? Scott Sauyet <scott.sauyet@gmail.com> - 2011-10-19 14:18 -0700
                Re: Objects comparaison ? Antony Scriven <adscriven@gmail.com> - 2011-10-19 15:46 -0700
                Objects comparison ? John G Harris <john@nospam.demon.co.uk> - 2011-10-20 16:28 +0100
                Re: Objects comparison ? Antony Scriven <adscriven@gmail.com> - 2011-10-20 12:23 -0700
                Re: Objects comparison ? Antony Scriven <adscriven@gmail.com> - 2011-10-20 15:04 -0700
                Re: Objects comparison ? John G Harris <john@nospam.demon.co.uk> - 2011-10-21 15:38 +0100
                Re: Objects comparison ? Andreas Bergmaier <andber93@web.de> - 2011-10-22 19:40 +0200
                Re: Objects comparison ? John G Harris <john@nospam.demon.co.uk> - 2011-10-23 11:49 +0100
                Re: Objects comparison ? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-10-24 19:00 +0200
                Re: Objects comparison ? Scott Sauyet <scott.sauyet@gmail.com> - 2011-10-21 05:29 -0700
                Re: Objects comparison ? John G Harris <john@nospam.demon.co.uk> - 2011-10-21 16:30 +0100
            Re: Objects comparaison ? Jukka Lahtinen <jtfjdehf@hotmail.com.invalid> - 2011-10-18 18:06 +0300
              Re: Objects comparaison ? Jake Jarvis <pig_in_shoes@yahoo.com> - 2011-10-18 17:43 +0200
      Re: Objects comparaison ? unbewusst.sein@fai.invalid (Une Bévue) - 2011-10-14 06:11 +0200
        Re: Objects comparaison ? "Jukka K. Korpela" <jkorpela@cs.tut.fi> - 2011-10-14 08:07 +0300
          Re: Objects comparaison ? unbewusst.sein@fai.invalid (Une Bévue) - 2011-10-14 07:31 +0200
            Re: Objects comparaison ? "Jukka K. Korpela" <jkorpela@cs.tut.fi> - 2011-10-14 08:59 +0300
              Re: Objects comparaison ? unbewusst.sein@fai.invalid (Une Bévue) - 2011-10-14 08:36 +0200
        Re: Objects comparaison ? unbewusst.sein@fai.invalid (Une Bévue) - 2011-10-14 08:35 +0200

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