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Groups > comp.lang.javascript > #39642

Re: input/output parameters

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Jon Ribbens:

> parseInt() - returns `NaN` on failure

I know and use it in my first attempt to get something like
out parameters:

   function tryparse_int_1(s, cb)
   {   var res = parseInt(s);
       cb(res);
       return !isNaN( res );
   }

   function test_1(s)
   {   var /* inreger */ i;
       if( tryparse_int_1( s, x=>i=x ) )
           console.log(`String "${s}" is parsed as integer ${i}.`); else
           console.log(`String "${s}" does not start with an integer.`);
   }

   test_1("47");
   test_1("forty-seven");

> Map.get() - returns `undefined` if the key isn't in the
> mapping

I see -- JS takes avail of its dymamic typing by returning
`undefined' for both mutable and immutable values, but that
approach requires two lines instead of one, i.e.:

   elem = map.get( key );
   if( elem == undefined )
   {  /*handle error*/   }

unless I use a feature of C-like languages that an
assignment is also an expression with a value:

   var /*integer*/ int;
   var /*boolean*/ ok;
   if( !isNaN(int = parseInt("5")) )
       console.log("ok: " + int); else
       console.log("not at int.");

> > while( read_next( stream, out element )
> > {       // process the element
> > }
> >
> > What alternative(s) does JavaScript propose?
>
> It would depend on the details of what you're doing. A lot
> of stream handling stuff in JavaScript was added before
> Promises, so you can't do the above and instead you'd be
> adding callbacks or event handlers.

I did not mean streams in particular but the programming of
a while loop that reads elements from a source until it is
exhausted. It may be rows from a recordset or tokens from a
string. I think I can do it this way:

   while( ( element = read_next( stream ) != undefined )
   {    // process the element
   }
   // or:
   while( true )
   {    element = read_next( stream )
        if( element == undefined ) break;
        // process the element
   }

But it is a choice between a bit clumsy and a bit wordy.

> Throw an exception on error then.

I generally dislike exceptions and try to use normal control-
flow instead.  My rule for exceptions is identical to
Joel's: catch them as early as possible, and never thow them
yourself:

   "Exceptions", by Joel Spolsky
   https://www.joelonsoftware.com/2003/10/13/13/

Ok, I do throw exceptions by way of asserts, if my program
can afford crashing at all.

> Or 'return data' from the function and use destructuring:
> [...]
>   const { multiplied, divided } = multiplyAndDivide(2, 4)
>   console.log(multiplied, divided)

Thanks for another alternative, I will certainly consider
it, although I find it somewhat aesthetically displeasing to
have more than one token on the left-hand side of an
assignment, but it may be better than passing several
anonymous setters or using eval:

   [ok, err_text, result] = get_temp_file();

This is shorter and cleaner than any of the alternatives I
know of.

> Or if you really, *really* want output arguments then, er,
> don't use JavaScript and use a different language that you
> like better instead.

Sometimes it is not an option. I am learning to live with
JavaScript.

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Thread

input/output parameters Anton Shepelev <anton.txt@gmail.com> - 2021-03-13 15:32 +0300
  Re: input/output parameters Jon Ribbens <jon+usenet@unequivocal.eu> - 2021-03-13 15:16 +0000
    Re: input/output parameters Anton Shepelev <anton.txt@gmail.com> - 2021-03-14 18:51 +0300
      Re: input/output parameters Jon Ribbens <jon+usenet@unequivocal.eu> - 2021-03-14 16:15 +0000
        Re: input/output parameters John G Harris <niam@jghnorth.org.uk.invalid> - 2021-03-14 18:31 +0000
          Re: input/output parameters Anton Shepelev <anton.txt@gmail.com> - 2021-03-14 22:27 +0300
            Re: input/output parameters Jon Ribbens <jon+usenet@unequivocal.eu> - 2021-03-14 23:44 +0000
            Re: input/output parameters "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2021-03-15 06:41 -0700
        Re: input/output parameters Anton Shepelev <anton.txt@gmail.com> - 2021-03-14 22:17 +0300
          Re: input/output parameters Jon Ribbens <jon+usenet@unequivocal.eu> - 2021-03-14 23:28 +0000
          Re: input/output parameters "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2021-03-15 06:39 -0700
      Re: input/output parameters Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-03-14 22:32 +0000
      Re: input/output parameters "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2021-03-15 06:36 -0700
        Re: input/output parameters Anton Shepelev <anton.txt@gmail.com> - 2021-03-20 14:49 +0300
          Re: input/output parameters "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2021-03-20 11:59 -0700
            Re: input/output parameters "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2021-03-20 13:07 -0700
          Re: input/output parameters John G Harris <niam@jghnorth.org.uk.invalid> - 2021-03-20 19:29 +0000
            Re: input/output parameters Jon Ribbens <jon+usenet@unequivocal.eu> - 2021-03-20 20:35 +0000
  Re: input/output parameters Anton Shepelev <anton.txt@gmail.com> - 2021-03-15 00:27 +0300
    Re: input/output parameters Jon Ribbens <jon+usenet@unequivocal.eu> - 2021-03-14 23:51 +0000
      Re: input/output parameters Anton Shepelev <anton.txt@gmail.com> - 2021-03-20 14:56 +0300
        Re: input/output parameters Jon Ribbens <jon+usenet@unequivocal.eu> - 2021-03-20 15:08 +0000
          Re: input/output parameters Anton Shepelev <anton.txt@gmail.com> - 2021-03-21 15:16 +0300
            Re: input/output parameters "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2021-03-21 08:46 -0700
              Re: input/output parameters Anton Shepelev <anton.txt@gmail.com> - 2021-04-10 14:54 +0300
        Re: input/output parameters "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2021-03-20 12:05 -0700
          Re: input/output parameters Anton Shepelev <anton.txt@gmail.com> - 2021-03-21 15:58 +0300
    Re: input/output parameters "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2021-03-15 06:43 -0700
    Re: input/output parameters Silvio <silvio@internet.com> - 2021-03-15 18:01 +0100
      Re: input/output parameters John G Harris <niam@jghnorth.org.uk.invalid> - 2021-03-16 18:06 +0000
        Re: input/output parameters Silvio <silvio@internet.com> - 2021-03-16 23:58 +0100
          Re: input/output parameters John G Harris <niam@jghnorth.org.uk.invalid> - 2021-03-17 19:14 +0000
            Re: input/output parameters Silvio <silvio@internet.com> - 2021-03-17 23:46 +0100
              Re: input/output parameters John G Harris <niam@jghnorth.org.uk.invalid> - 2021-03-18 18:04 +0000
                Re: input/output parameters Silvio <silvio@internet.com> - 2021-03-22 00:39 +0100
                Re: input/output parameters John G Harris <niam@jghnorth.org.uk.invalid> - 2021-03-23 10:44 +0000
                Re: input/output parameters Silvio <silvio@internet.com> - 2021-03-30 00:33 +0200
                Re: input/output parameters John G Harris <niam@jghnorth.org.uk.invalid> - 2021-03-31 19:53 +0100
                Re: input/output parameters Silvio <silvio@internet.com> - 2021-04-01 01:17 +0200
                Re: input/output parameters John G Harris <niam@jghnorth.org.uk.invalid> - 2021-04-01 18:02 +0100
      Re: input/output parameters Anton Shepelev <anton.txt@gmail.com> - 2021-03-20 15:50 +0300
        Re: input/output parameters John G Harris <niam@jghnorth.org.uk.invalid> - 2021-03-20 18:52 +0000
          Re: input/output parameters Anton Shepelev <anton.txt@gmail.com> - 2021-03-21 17:35 +0300
            Re: input/output parameters "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2021-03-21 08:50 -0700
              Re: input/output parameters Anton Shepelev <anton.txt@gmail.com> - 2021-03-21 19:31 +0300
            Re: input/output parameters John G Harris <niam@jghnorth.org.uk.invalid> - 2021-03-21 19:27 +0000
        Re: input/output parameters "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2021-03-20 13:02 -0700
  Re: input/output parameters Postiljon Petskin <yyyyyyyyyyyywwwww@zohomail.eu> - 2023-04-22 08:47 -0700

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