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Re: Bubblesort

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Stefan Weiss wrote:

> On 03/08/2016 23:35, Thomas 'PointedEars' Lahn wrote:
>> Stefan Weiss wrote:
>>> Alternatively, you can sort string array elements using a numeric
>>> comparison function:
>>>
>>>     arr[x].nodelinks.sort((a, b) => a - b);
>>>
>>> Or in a more verbose form (but with better UA compatibility):
>>>
>>>     function compareNumeric (a, b)
>>>     {
>>>         return a - b;
>>>     }
>>>
>>>     arr[x].nodelinks.sort(compareNumeric);
>> 
>> For reasonable backwards-compatibility, the function declaration is
>> unnecessary/unwise, unless the comparator is declared locally *and* used
>> locally more than once (in which case a function declaration/variable
>> initialization saves memory).
> 
> In this case, sort() is used in a loop.

Then a local variable declaration with initialization (see below) or a local 
function declaration is appropriate, unless the function makes an closure 
over a name with a loop-variant value.

>> Function expressions are backwards-compatible down to JavaScript 1.3 and
>> JScript 5.0 at least (Netscape Navigator 4.06+, Internet Explorer 5.0), 
>> therefore marked “safe” in the ECMAScript Support Matrix since its 
>> inception in 2005 (IIRC).
> 
> I didn't mean to say that function declarations were more compatible
> than function expressions.

Nor did I imply that you did.

> The second example is also "more verbose", it was intended to show how a
> common comparison function can be made reusable.

That was reasonable, given the context of the question that I could not see 
(and did not want to consider here anyway).
 
> The difference in memory usage should be minimal. A declared function
> will remain in memory at least until it goes out of scope and can be
> garbage collected (when no references to it are left). With function
> expressions, no reference to the function is left after it has been used
> to sort the array. I don't expect a measureable difference either way.

I was recommending that if you need the same comparator more than once, you 
should not do so by using the same function expression more than once in an 
argument list.  So not

  var
    a = [3, 1, 2],
    b = [5, 6, 4],
    c = [8, 9, 7];

  a.sort(function (x, y) { return x - y; });
  b.sort(function (x, y) { return x - y; });
  c.sort(function (x, y) { return x - y; });

but instead

  var
    a = [3, 1, 2],
    b = [5, 6, 4],
    c = [8, 9, 7],
    f = function (x, y) { return x - y; };

  a.sort(f);
  b.sort(f);
  c.sort(f);

That an object is no longer referred to does not mean that it has been 
garbage-collected, so WLOG one must assume that every evaluation of a 
function expression creates a new object with the "old" one still reserving 
memory.

There might be internal optimizations in some implementations that would not 
create a new Function instance for the *same* function expression (but it 
would not be trivial to implement this, because of the closure); but it is 
unwise to rely on that.

BTW, who would be interested in a sort method that would be able to only 
sort parts of an array?
 
> OT: You didn't mention performance, but I was curious and did a quick
> test anyway: in current versions of Firefox and Chrome, there are no
> huge differences, although referencing a previously created function is
> consistently faster than using an inline expression,

I expected that.

> and traditional functions are consistently faster than arrow functions.

I did not expect that …

> In Firefox 44, inline arrow functions are noticably slower than the other
> variants (about an order of magnitude).

… that – so, are we, in the end, sacrificing performance for convenient 
syntax with arrow functions here? –,
 
> By the way, const/let are also consistently slower than var, but not by
> much. This may be caused by the additional checks required for the
> "temporal dead zone".

… or that.  Thank you for sharing this.

-- 
PointedEars
FAQ: <http://PointedEars.de/faq> | SVN: <http://PointedEars.de/wsvn/>
Twitter: @PointedEars2 | ES Matrix: <http://PointedEars.de/es-matrix>
Please do not cc me. / Bitte keine Kopien per E-Mail.

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Bubblesort jonas.thornvall@gmail.com - 2016-03-04 02:00 -0800
  Re: Bubblesort "Mr. Man-wai Chang" <toylet.toylet@gmail.com> - 2016-03-04 18:53 +0800
    Re: Bubblesort "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2016-03-04 12:01 +0100
      Re: Bubblesort jonas.thornvall@gmail.com - 2016-03-04 03:03 -0800
      Re: Bubblesort jonas.thornvall@gmail.com - 2016-03-04 05:15 -0800
        Re: Bubblesort jonas.thornvall@gmail.com - 2016-03-04 05:41 -0800
          Re: Bubblesort "Mr. Man-wai Chang" <toylet.toylet@gmail.com> - 2016-03-04 21:56 +0800
          Re: Bubblesort Stefan Weiss <krewecherl@gmail.com> - 2016-03-04 15:10 +0100
            Re: Bubblesort jonas.thornvall@gmail.com - 2016-03-04 07:37 -0800
              Re: Bubblesort Stefan Weiss <krewecherl@gmail.com> - 2016-03-04 17:08 +0100
            Re: Bubblesort jonas.thornvall@gmail.com - 2016-03-04 07:50 -0800
            Re: Bubblesort jonas.thornvall@gmail.com - 2016-03-04 07:54 -0800
              Re: Bubblesort Stefan Weiss <krewecherl@gmail.com> - 2016-03-04 17:21 +0100
              Re: Bubblesort Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-03-04 19:26 +0000
                Re: Bubblesort "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2016-03-04 23:05 +0100
                Re: Bubblesort jonas.thornvall@gmail.com - 2016-03-05 09:15 -0800
                Re: Bubblesort Stefan Weiss <krewecherl@gmail.com> - 2016-03-08 03:43 +0100
                Re: Bubblesort jonas.thornvall@gmail.com - 2016-03-08 02:41 -0800
                Re: Bubblesort jonas.thornvall@gmail.com - 2016-03-08 09:10 -0800
                Re: Bubblesort Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-03-08 23:34 +0100
                Re: Bubblesort Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-03-08 23:46 +0100
                Re: Bubblesort Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-03-09 00:16 +0000
                Re: Bubblesort Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-03-09 02:41 +0100
            Re: Bubblesort Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-03-08 23:35 +0100
              Re: Bubblesort Stefan Weiss <krewecherl@gmail.com> - 2016-03-09 02:38 +0100
                Re: Bubblesort Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-03-09 22:04 +0100
                Re: Bubblesort Stefan Weiss <krewecherl@gmail.com> - 2016-03-10 21:14 +0100
                Re: Bubblesort Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-03-10 22:17 +0100
                Re: Bubblesort "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2016-03-10 22:31 +0100
                Re: Bubblesort Stefan Weiss <krewecherl@gmail.com> - 2016-03-10 23:25 +0100
                Re: Bubblesort "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2016-03-11 00:16 +0100
        Re: Bubblesort "Mr. Man-wai Chang" <toylet.toylet@gmail.com> - 2016-03-04 21:59 +0800
          Re: Bubblesort "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2016-03-04 17:12 +0100
          Re: Bubblesort Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-03-05 02:00 +0100
            Re: Bubblesort John Harris <niam@jghnorth.org.uk.invalid> - 2016-03-05 18:39 +0000
            Re: Bubblesort Scott Sauyet <scott.sauyet@gmail.com> - 2016-03-05 17:40 -0800
      Re: Bubblesort "Mr. Man-wai Chang" <toylet.toylet@gmail.com> - 2016-03-04 21:54 +0800
        Re: Bubblesort "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2016-03-04 16:59 +0100
    Re: Bubblesort jonas.thornvall@gmail.com - 2016-03-04 03:04 -0800
      Re: Bubblesort jonas.thornvall@gmail.com - 2016-03-04 03:55 -0800
    Re: Bubblesort Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-03-05 00:01 +0100
      Re: Bubblesort Aleksandro <aleksandro@gmx.com> - 2016-03-06 18:41 -0300

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