Re: Programming style question

Message-ID	<3469358.shaKaQI8qd@PointedEars.de> (permalink)
From	Thomas 'PointedEars' Lahn <PointedEars@web.de>
Organization	PointedEars Software (PES)
Date	2012-10-24 01:15 +0100
Subject	Re: Programming style question
Newsgroups	comp.lang.javascript
References	<r_WdnX50haYCLeLNnZ2dnUVZ_vGdnZ2d@earthlink.com> <1538954.egObkdgl4n@PointedEars.de> <cfCdnQ0lM4FWbeLNnZ2dnUVZ_rmdnZ2d@earthlink.com> <k5ost7$d7o$1@dont-email.me> <0qGdnW4DceWJZeLNnZ2dnUVZ_gadnZ2d@earthlink.com>
Followup-To	comp.lang.javascript

Followups directed to: comp.lang.javascript

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Patricia Shanahan wrote:

> Jukka K. Korpela wrote:
>> A formal parameter has no type. Its values may have types. When you call
>> foo(42), then the formal parameter gets the value 42, a number. When you
>> call foo('a'), it gets the value 'a', a string. There is no point in
>> confusing this by saying that parameters or variables have types.
> 
> So your position is that a variable always has a value, possibly the
> undefined value, and the type belongs to the current value. Is that
> correct?

Your understanding is correct; your understanding of the position is not, 
because the position is not correct.

Like a local variable, a formal parameter only has meaning in the local 
execution context of the function.  There it does have a type: the type of 
the argument that was passed for it, if any.

It is important to know the difference between arguments and (formal) 
parameters.  A function can be passed arguments for which there is no formal 
(named) parameter; those can be accessed with the arguments object.  On the 
other hand, the type of a parameter for which no argument has been passed is 
Undefined.

Similarly, any variable has a type at runtime: the type of the expression at 
last assignment (which may be Undefined), or Undefined.  If it was not 
initialized, i. e. had never been assigned a value explicitly, its type was 
Undefined.  

In

  /**
   * Foos a bar and returns it.
   *
   * @param x : Object|String
   * @param y : Number
   * @return {String} The fooed bar.
   */
  function foo (x, y)
  {
    var z;
    console.log(x, y, arguments[2], z);
    return x;
  }

  foo(bar, baz, 42);

`foo' is the function identifier, and the values of `bar' and `baz' are 
arguments to the function.  `x' and `y' are formal parameters of the 
function for which the values of `bar' and `baz' have been passed as 
arguments.  A third argument has been passed to the function which is not 
accessible by name (because there is no parameter for it), but through the 
`arguments' object; its `2' property specifies that third argument (0-based 
indexing).  The types of `x' and `y' at runtime are the types of the values 
of `bar' and `baz', respectively.  The value of `z' is `undefined', of type 
Undefined, at runtime *here*, because it would have been never assigned a 
value explicitly.

The *expected* types for those parameters are to be documented, so that the 
function/method can be used properly.  IOW, a user of the function should 
not expect it to work properly if arguments of an undocumented type had been 
passed (but they can expect the function to be callable).  (AISB, be very 
careful with overloading.)

>> However, it is essential to note that the mechanisms of the language do
>> not protect you from "type errors" in the sense as in many other
>> languages where you get a compile-time or run-time message about
>> assignment of a value of a wrong type.

Correct.  That follows from the languages using *dynamic* (run-time) typing 
as opposed to *static* (compile-time) typing.

>> Neither do you get automatic type conversions based on the type of a
>> variable - simply because variables do not have types in JavaScript.

Nonsense.  AISB, all variables do have a type.  They only do not have a 
(specific) type at compile time.  They do have one *at runtime*.

PointedEars
-- 
Anyone who slaps a 'this page is best viewed with Browser X' label on
a Web page appears to be yearning for the bad old days, before the Web,
when you had very little chance of reading a document written on another
computer, another word processor, or another network. -- Tim Berners-Lee

Thread

Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-18 08:32 +0100
  Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-18 10:23 +0200
    Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-18 13:42 +0100
      Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-18 17:59 +0200
        Re: Programming style question Gene Wirchenko <genew@ocis.net> - 2012-10-18 09:56 -0700
          Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-19 00:49 +0200
            Re: Programming style question Gene Wirchenko <genew@ocis.net> - 2012-10-19 11:04 -0700
              Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-20 11:52 +0200
            Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-19 12:06 -0700
              Re: Programming style question Tim Streater <timstreater@greenbee.net> - 2012-10-19 23:12 +0100
                Re: Programming style question "Mel Smith" <med_cutout_syntel@aol.com> - 2012-10-19 21:56 -0600
              Re: Programming style question Bart Van der Donck <bart@nijlen.com> - 2012-10-20 02:21 -0700
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-20 12:03 +0200
                Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-20 06:31 -0700
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-20 18:30 +0200
                Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-20 10:32 -0700
                Re: Programming style question Tim Streater <timstreater@greenbee.net> - 2012-10-20 22:34 +0100
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-21 10:12 +0200
                Re: Programming style question Tim Streater <timstreater@greenbee.net> - 2012-10-21 09:34 +0100
                Re: Programming style question Dr J R Stockton <reply1242@merlyn.demon.co.uk.invalid> - 2012-10-21 17:59 +0100
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-22 09:55 +0200
                Re: Programming style question Tim Streater <timstreater@greenbee.net> - 2012-10-22 09:50 +0100
                Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-22 04:49 -0700
                Re: Programming style question Tim Streater <timstreater@greenbee.net> - 2012-10-22 14:04 +0100
                Re: Programming style question Hans-Georg Michna <hans-georgNoEmailPlease@michna.com> - 2012-10-22 16:07 +0200
                Re: Programming style question Dr J R Stockton <reply1243@merlyn.demon.co.uk.invalid> - 2012-10-23 18:22 +0100
                Re: Programming style question Hans-Georg Michna <hans-georgNoEmailPlease@michna.com> - 2012-10-22 16:01 +0200
                Re: Programming style question Jim T. <x@y.z> - 2012-10-22 12:16 -0400
                Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-22 11:40 -0700
                Re: Programming style question Gene Wirchenko <genew@ocis.net> - 2012-10-22 14:01 -0700
                Re: Programming style question Hans-Georg Michna <hans-georgNoEmailPlease@michna.com> - 2012-10-23 10:07 +0200
                Re: Programming style question Gene Wirchenko <genew@ocis.net> - 2012-10-23 09:43 -0700
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-23 11:49 +0200
                Re: Programming style question Jim T. <x@y.z> - 2012-10-23 15:52 -0400
                Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-23 13:07 -0700
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-23 22:45 +0200
                Re: Programming style question Gene Wirchenko <genew@ocis.net> - 2012-10-23 14:14 -0700
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-24 09:35 +0200
                Re: Programming style question Gene Wirchenko <genew@ocis.net> - 2012-10-24 10:17 -0700
                Re: Programming style question Dr J R Stockton <reply1243@merlyn.demon.co.uk.invalid> - 2012-10-25 18:41 +0100
                Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-25 17:03 -0700
                Re: Programming style question Gene Wirchenko <genew@ocis.net> - 2012-10-25 20:14 -0700
                Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-25 20:46 -0700
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-26 09:55 +0200
                Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-26 06:18 -0700
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-26 17:43 +0200
                Re: Programming style question Gene Wirchenko <genew@ocis.net> - 2012-10-26 09:57 -0700
                Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-26 10:24 -0700
                Re: Programming style question Gene Wirchenko <genew@ocis.net> - 2012-10-26 14:18 -0700
                Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-27 10:45 +0200
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-27 12:58 +0200
                Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-27 16:18 +0200
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-27 18:08 +0200
                Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-27 18:26 +0200
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-27 19:43 +0200
                Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-27 21:09 +0200
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-27 22:53 +0200
                Re: Programming style question John G Harris <john@nospam.demon.co.uk> - 2012-10-28 11:37 +0000
                Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-28 12:50 +0100
                Re: Programming style question Martin Leese <please@see.Web.for.e-mail.INVALID> - 2012-10-28 13:43 -0600
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-28 23:58 +0100
                Re: Programming style question John G Harris <john@nospam.demon.co.uk> - 2012-10-29 11:18 +0000
                Re: Programming style question Eric Bednarz <bednarz@fahr-zur-hoelle.org> - 2012-10-27 23:58 +0200
                Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-28 12:43 +0100
                Re: Programming style question Dr J R Stockton <reply1243@merlyn.demon.co.uk.invalid> - 2012-10-27 19:44 +0100
                Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-24 12:06 -0700
                Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-24 21:27 +0200
                Re: Programming style question Gene Wirchenko <genew@ocis.net> - 2012-10-24 15:12 -0700
                Re: Programming style question Tim Streater <timstreater@greenbee.net> - 2012-10-25 01:29 +0100
                Re: Programming style question Stefan Weiss <krewecherl@gmail.com> - 2012-10-24 21:25 +0200
                Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-24 21:57 +0200
                Re: Programming style question Stefan Weiss <krewecherl@gmail.com> - 2012-10-25 01:11 +0200
                Re: Programming style question Christoph Becker <cmbecker69@gmx.de> - 2012-10-25 02:00 +0200
                Re: Programming style question Scott Sauyet <scott.sauyet@gmail.com> - 2012-10-24 20:27 -0700
                Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-25 08:44 +0200
                Re: Programming style question Adam Silver <adambsilver@gmail.com> - 2012-10-25 04:28 -0700
                Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-25 23:18 +0200
                Re: Programming style question Scott Sauyet <scott.sauyet@gmail.com> - 2012-10-26 08:24 -0700
                Re: Programming style question Stefan Weiss <krewecherl@gmail.com> - 2012-11-07 22:13 +0100
                Re: Programming style question Tim Streater <timstreater@greenbee.net> - 2012-11-07 21:51 +0000
                Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-11-07 23:47 +0100
                Re: Programming style question Stefan Weiss <krewecherl@gmail.com> - 2012-11-08 01:14 +0100
                Re: Programming style question Gene Wirchenko <genew@ocis.net> - 2012-11-07 16:51 -0800
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-11-08 16:45 +0100
                Re: Programming style question Scott Sauyet <scott.sauyet@gmail.com> - 2012-11-08 08:02 -0800
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-11-08 17:39 +0100
                Re: Programming style question Gene Wirchenko <genew@ocis.net> - 2012-11-08 11:25 -0800
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-11-08 22:25 +0100
                Re: Programming style question John G Harris <john@nospam.demon.co.uk> - 2012-11-09 10:19 +0000
                Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-11-09 17:41 +0100
                Re: Programming style question Dr J R Stockton <reply1245@merlyn.demon.co.uk.invalid> - 2012-11-10 22:38 +0000
                Re: Programming style question Scott Sauyet <scott.sauyet@gmail.com> - 2012-10-22 12:32 -0700
                Re: Programming style question Hans-Georg Michna <hans-georgNoEmailPlease@michna.com> - 2012-10-23 10:05 +0200
                Re: Programming style question Christoph Becker <cmbecker69@gmx.de> - 2012-10-22 22:11 +0200
                Re: Programming style question Stefan Weiss <krewecherl@gmail.com> - 2012-10-23 02:42 +0200
                Re: Programming style question Hans-Georg Michna <hans-georgNoEmailPlease@michna.com> - 2012-10-23 10:08 +0200
              Re: Programming style question "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-10-20 18:34 +0200
  Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-18 11:57 +0200
    Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-18 13:06 +0100
      Re: Programming style question "Jukka K. Korpela" <jkorpela@cs.tut.fi> - 2012-10-18 15:32 +0300
        Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-18 13:37 +0100
          Re: Programming style question "Jukka K. Korpela" <jkorpela@cs.tut.fi> - 2012-10-18 15:55 +0300
          Re: Programming style question John G Harris <john@nospam.demon.co.uk> - 2012-10-19 10:12 +0100
            Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-19 07:24 -0700
              Re: Programming style question John G Harris <john@nospam.demon.co.uk> - 2012-10-20 17:47 +0100
          Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-24 01:15 +0100
            Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-24 01:31 +0100
            Re: Programming style question "Jukka K. Korpela" <jkorpela@cs.tut.fi> - 2012-10-24 07:34 +0300
              Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-24 19:57 +0200
                Re: Programming style question "Jukka K. Korpela" <jkorpela@cs.tut.fi> - 2012-10-24 21:02 +0300
        Re: Programming style question Patricia Shanahan <pats@acm.org> - 2012-10-18 20:15 -0700
      Re: Programming style question Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-10-24 01:21 +0100
  Re: Programming style question Scott Sauyet <scott.sauyet@gmail.com> - 2012-10-21 17:57 -0700

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