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Function arguments vs. local variables (was: Difference between findPos("divThis") and findPos(divThis))

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Frobernik wrote:

> Thomas 'PointedEars' Lahn wrote:
>> Frobernik wrote:
>>> function findPos(obj, name, colour, b, c) {
>>>       name = obj.name;
>>>       colour = obj.colour;
>>>       b = 17;
>>>       c = [{s:'monkey', x:'male', a:3}, {s:'elephant',x:'female',a:7}];
>>> }
>>> findPos({name:'df', colour:'green'})
>>
>> We have been over this.
> 
> We have?

Yes.  We, the previous subscribers of this newsgroup, have.  You should read 
a fair amount of past discussions before you post to a newsgroup:

<http://jibbering.com/faq/notes/posting>
 
>> Declaring arguments instead of local variables may be great for code
>> golfing (140 characters maximum), but it is a Really Bad Idea for all
>> other code. To begin with, by looking at the code you cannot tell whether
>> you are modifying an argument or not.  Editors and linters which can
>> differentiate between arguments and local variables could not tell as
>> well.
> 
> An editor or linters not going to know more about my code than me

Whether that is true depends on what you *actually* know about your code.

I know at least one ECMAScript-supporting editor, which includes a linter, 
that can differentiate between function arguments and local variables: 
Eclipse JavaScript Developer Tools (JSDT).

It is rather obvious that this is possible for a machine because each 
/FunctionDeclaration/ or /FunctionExpression/ has an argument list, and 
identifiers need to be *declared* variable names in order to be *variable* 
names.  So the following heuristics can be applied to a standalone 
/IdentifierName/ within a function body:

N¹ A  V  I  B  Meaning
-------------------------------------------------------------------------
−  −  −  −  +  Probable ReferenceError (all modes)
−  −  −  +  +  Possible "Implied global", i. e. property of an object in
               the function scope's scope chain created; possible
               ReferenceError (strict mode)
−  −  +  −  −  Local variable, unused
−  −  +  −  +  Local variable, used
−  −  +  +  +  Local variable (initialized), used
–  +  −  −  –  Function argument, unused
–  +  −  −  +  Function argument, used
−  +  −  +  +  Function argument (used), possible default value init.
−  +  +  −  −  Local variable (unused), hiding a function argument
−  +  +  −  +  Local variable (used, uninitialized), hiding a function
               argument
−  +  +  +  +  Local variable (used), hiding a function argument
+  −  −  −  −  Non-local property or variable
+  −  −  −  +  Property in the function scope's scope chain (perhaps
               uninitialized), used
+  −  −  +  +  Property in the function scope's scope chain, used
+  −  +  −  −  Local variable (unused), hiding a property in the
               function scope's scope chain
+  −  +  −  +  Local variable (used, uninitialized), perhaps hiding a
               property in the function scope's scope chain
+  −  +  +  +  Local variable (used), hiding a property in the
               function scope's scope chain
+  +  −  −  –  Function argument (unused), perhaps hiding a property in the
               function scope's scope chain
+  +  −  −  +  Function argument (used), perhaps hiding a property in the
               function scope's scope chain
+  +  −  +  +  Function argument (used, perhaps assigned to), perhaps hiding
               a property in the function scope's scope chain
+  +  +  −  −  Local variable (unused), hiding a function argument,
               which hides a property in the function scope's scope chain
+  +  +  −  +  Local variable (used), hiding a function argument,
               which hides a property in the function scope's scope chain
+  +  +  +  +  Local variable (used, initialized), hiding a function
               argument, which hides a property in the function scope's
               scope chain
_____
¹) N: Non-local occurence
   A: Occurence in function's argument list
   V: VariableDeclaration in function body
   I: Initialization/assignment in function body
   B: Occurence in function body
   +: Applies
   −: Does not apply

In an implementation of similar heuristics, Eclipse JSDT allows function 
arguments and variables to be displayed differently.  For example, I have 
set it up so that it would display argument declarations and references in 
bluish italic characters; the identifier in variable declarations in regular 
style, but underlined; and local variable references in normal-colored 
italic characters.  If I were to use your approach, I could not tell at a 
glance if an identifier was an argument or a local variable name.  I could 
be ending up assigning to arguments, inadvertently altering the program flow 
after that assignment.  If someone would call my function, and I would 
forget to assign to the argument but used it later, they could, 
intentionally or accidentally, alter the inner workings of my function.

AISB, a Really Bad Idea for a number of reasons, another one being that in 
an API you only expose to the world what needs to be exposed to it.


PointedEars
-- 
Use any version of Microsoft Frontpage to create your site.
(This won't prevent people from viewing your source, but no one
will want to steal it.)
  -- from <http://www.vortex-webdesign.com/help/hidesource.htm> (404-comp.)

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Difference between findPos("divThis") and findPos(divThis) " Cal Who" <CalWhoNOSPAM@roadrunner.com> - 2011-11-13 09:51 -0500
  Re: Difference between findPos("divThis") and findPos(divThis) Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-11-13 18:25 +0100
    Re: Difference between findPos("divThis") and findPos(divThis) " Cal Who" <CalWhoNOSPAM@roadrunner.com> - 2011-11-13 13:58 -0500
      Re: Difference between findPos("divThis") and findPos(divThis) Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-11-13 20:26 +0100
        Re: Difference between findPos("divThis") and findPos(divThis) " Cal Who" <CalWhoNOSPAM@roadrunner.com> - 2011-11-13 15:04 -0500
          Re: Difference between findPos("divThis") and findPos(divThis) "J.R." <groups_jr-1@yahoo.com.br> - 2011-11-13 18:55 -0200
            Re: Difference between findPos("divThis") and findPos(divThis) "J.R." <groups_jr-1@yahoo.com.br> - 2011-11-13 18:59 -0200
              Re: Difference between findPos("divThis") and findPos(divThis) " Cal Who" <CalWhoNOSPAM@roadrunner.com> - 2011-11-13 17:10 -0500
                Re: Difference between findPos("divThis") and findPos(divThis) "J.R." <groups_jr-1@yahoo.com.br> - 2011-11-13 20:49 -0200
                Re: Difference between findPos("divThis") and findPos(divThis) " Cal Who" <CalWhoNOSPAM@roadrunner.com> - 2011-11-13 20:00 -0500
                Re: Difference between findPos("divThis") and findPos(divThis) Denis McMahon <denismfmcmahon@gmail.com> - 2011-11-14 02:37 +0000
                Re: Difference between findPos("divThis") and findPos(divThis) "J.R." <groups_jr-1@yahoo.com.br> - 2011-11-14 03:14 -0200
                Re: Difference between findPos("divThis") and findPos(divThis) Denis McMahon <denismfmcmahon@gmail.com> - 2011-11-14 14:03 +0000
                Re: Difference between findPos("divThis") and findPos(divThis) "J.R." <groups_jr-1@yahoo.com.br> - 2011-11-14 14:14 -0200
                Re: Difference between findPos("divThis") and findPos(divThis) Denis McMahon <denismfmcmahon@gmail.com> - 2011-11-14 18:31 +0000
                Re: Difference between findPos("divThis") and findPos(divThis) "Evertjan." <exjxw.hannivoort@interxnl.net> - 2011-11-14 18:36 +0000
                Re: Difference between findPos("divThis") and findPos(divThis) Denis McMahon <denismfmcmahon@gmail.com> - 2011-11-15 00:18 +0000
                Re: Difference between findPos("divThis") and findPos(divThis) Scott Sauyet <scott.sauyet@gmail.com> - 2011-11-14 10:54 -0800
                Re: Difference between findPos("divThis") and findPos(divThis) "Richard Cornford" <Richard@litotes.demon.co.uk> - 2011-11-15 01:23 +0000
                Re: Difference between findPos("divThis") and findPos(divThis) Scott Sauyet <scott.sauyet@gmail.com> - 2011-11-16 06:04 -0800
                Re: Difference between findPos("divThis") and findPos(divThis) Frobernik <nospam@nospam.com> - 2011-11-17 22:06 +0000
                Re: Difference between findPos("divThis") and findPos(divThis) Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-11-17 23:54 +0100
                Re: Difference between findPos("divThis") and findPos(divThis) Frobernik <nospam@nospam.com> - 2011-11-18 09:33 +0000
                Function arguments vs. local variables (was: Difference between findPos("divThis") and findPos(divThis)) Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-11-19 16:05 +0100
                Re: Function arguments vs. local variables Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-11-19 18:17 +0100
                Re: Function arguments vs. local variables Frobernik <nospam@nospam.com> - 2011-11-21 20:01 +0000
                Re: Function arguments vs. local variables Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-11-22 12:50 +0100
                Re: Difference between findPos("divThis") and findPos(divThis) Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-11-14 15:04 +0100
                Re: Difference between findPos("divThis") and findPos(divThis) John G Harris <john@nospam.demon.co.uk> - 2011-11-14 15:13 +0000
                Re: Difference between findPos("divThis") and findPos(divThis) Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-11-14 18:27 +0100
                Re: Difference between findPos("divThis") and findPos(divThis) Eric Bednarz <bednarz@fahr-zur-hoelle.org> - 2011-11-14 17:52 +0100
                Re: Difference between findPos("divThis") and findPos(divThis) "J.R." <groups_jr-1@yahoo.com.br> - 2011-11-14 15:07 -0200
                Re: Difference between findPos("divThis") and findPos(divThis) Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-11-14 18:19 +0100
                Re: Difference between findPos("divThis") and findPos(divThis) "J.R." <groups_jr-1@yahoo.com.br> - 2011-11-14 15:44 -0200
                Re: Difference between findPos("divThis") and findPos(divThis) Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-11-14 19:01 +0100
                Re: Difference between findPos("divThis") and findPos(divThis) "J.R." <groups_jr-1@yahoo.com.br> - 2011-11-14 16:42 -0200
                Re: Difference between findPos("divThis") and findPos(divThis) Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-11-14 19:53 +0100
                Re: Difference between findPos("divThis") and findPos(divThis) Richard Cornford <Richard@litotes.demon.co.uk> - 2011-11-14 09:18 -0800
                Re: Difference between findPos("divThis") and findPos(divThis) "J.R." <groups_jr-1@yahoo.com.br> - 2011-11-14 16:22 -0200
                Re: Difference between findPos("divThis") and findPos(divThis) Denis McMahon <denismfmcmahon@gmail.com> - 2011-11-14 18:38 +0000
                Re: Difference between findPos("divThis") and findPos(divThis) Gene Wirchenko <genew@ocis.net> - 2011-11-14 12:12 -0800
                Re: Difference between findPos("divThis") and findPos(divThis) Gene Wirchenko <genew@ocis.net> - 2011-11-14 12:00 -0800
                Re: Difference between findPos("divThis") and findPos(divThis) " Cal Who" <CalWhoNOSPAM@roadrunner.com> - 2011-11-14 08:48 -0500
                Re: Difference between findPos("divThis") and findPos(divThis) Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-11-14 13:15 +0100
                Re: Difference between findPos("divThis") and findPos(divThis) "J.R." <groups_jr-1@yahoo.com.br> - 2011-11-14 13:03 -0200
                Re: Difference between findPos("divThis") and findPos(divThis) Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-11-14 17:24 +0100
          Re: Difference between findPos("divThis") and findPos(divThis) Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-11-14 13:00 +0100
        Re: Difference between findPos("divThis") and findPos(divThis) John G Harris <john@nospam.demon.co.uk> - 2011-11-14 15:05 +0000

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