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Re: class needs to initialize vars, set data structure

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Thomas 'PointedEars' Lahn wrote:

> Stefan Ram wrote:
>> ram@zedat.fu-berlin.de (Stefan Ram) writes:
>>> var Set = function()
> […]
>>> { var map = {};
>>>  return
>>>  { add     : function( element ){ map[ element ]= true; },
> […]
>>>    remove  : function( element ){ delete map[ element ]; },
> […]
>>>    contains: function( element ){ return map.hasOwnProperty( element );
> […]
>>>    },
>>>    count   : function( element ){ return Object.keys( map ).length; }
> […]
>>>    }};
> […]
> Compare <http://PointedEars.de/wsvn/JSX/trunk/map.js>.
> […]
> Also, a set is _not_ a map, and vice-versa.  A set is a data structure
> that contains no duplicate *values*; a map is a data structure that
> contains no duplicate *keys*.

Reviewing this, I see that you are probably aware of that fact as the 
“true” indicates that you intended your “Set” factory to work that way.

However, you are not aware of the fact that property names are, and can only 
be, primitive String values in ECMAScript.  Non-strings are converted to 
String for property access. [1]  So this works reliably only for String 
values, *with the provisions that I named*.

AFAICS, a reliable *and* efficient Set implementation in ECMAScript leads to 
a hash table implementation where the key is the string representation of 
the value (while avoiding to overwrite built-in properties), and each entry 
of the table contains no duplicates.  IOW, for this a Map implementation is 
required that supports non-strings as keys.

Incidentally, that is what jsx.map.Map() does, so I had used it in 
jsx.python.set(), which I had completely forgotten about:

<http://PointedEars.de/wsvn/JSX/trunk/python.js>
<http://PointedEars.de/scripts/test/python>

(This code is on “trunk”, therefore largely untested and not stable;
bug reports are appreciated.)

__________
[1] <http://ecma-international.org/ecma-262/5.1/#sec-11.2.1>
-- 
PointedEars
FAQ: <http://PointedEars.de/faq> | SVN: <http://PointedEars.de/wsvn/>
Twitter: @PointedEars2 | ES Matrix: <http://PointedEars.de/es-matrix>
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class needs to initialize vars, set data structure JRough <janis.rough@gmail.com> - 2014-03-11 15:36 -0700
  Re: class needs to initialize vars, set data structure Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-03-12 03:34 +0100
    Re: class needs to initialize vars, set data structure Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-03-12 15:09 +0100
    Re: class needs to initialize vars, set data structure John Harris <niam@jghnorth.org.uk.invalid> - 2014-03-12 17:04 +0000
      Re: class needs to initialize vars, set data structure John Harris <niam@jghnorth.org.uk.invalid> - 2014-03-14 10:48 +0000
  Re: class needs to initialize vars, set data structure Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-03-12 03:17 +0000
    Re: class needs to initialize vars, set data structure Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-03-12 11:46 +0100
    Re: class needs to initialize vars, set data structure Christoph Michael Becker <cmbecker69@arcor.de> - 2014-06-25 22:51 +0200
      Re: class needs to initialize vars, set data structure Christoph Michael Becker <cmbecker69@arcor.de> - 2014-06-26 00:42 +0200
        Re: class needs to initialize vars, set data structure Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-06-26 11:16 +0200
        Re: class needs to initialize vars, set data structure Christoph Michael Becker <cmbecker69@arcor.de> - 2014-06-26 21:44 +0200
          Re: class needs to initialize vars, set data structure John Harris <niam@jghnorth.org.uk.invalid> - 2014-06-27 09:46 +0100
            Re: class needs to initialize vars, set data structure Scott Sauyet <scott.sauyet@gmail.com> - 2014-06-28 21:57 -0700
  Re: class needs to initialize vars, set data structure Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-03-12 15:34 +0100

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