Constant keyword, does it have use when I create code for myself?

[guinness]

In my pursuit of applying 'good coding practice' to AutoIt, I draw your attention to the Const keyword and ask whether I should I use it in my own code when I already have an understanding of what the code is doing? Or should I use it for the purposes of debugging as Au3Check will flag a syntax error?

#include <Constants.au3>

Example()

Func Example()
    Local $sMessage = 'Some message that is assigned to a variable which won''t be changed i.e. constant variable.' ; This won't change
    Local $iVar = 0 ; This variable in local scope will be changed.

    For $i = 1 To 10
        $iVar += 1
    Next
    MsgBox($MB_SYSTEMMODAL, '$iVar=' & $iVar, $sMessage)
EndFunc   ;==>Example

OR should I use it regardless?

#include <Constants.au3>

Example()

Func Example()
    Local Const $sMessage = 'Some message that is assigned to a variable which won''t be changed i.e. constant variable.' ; This won't change
    Local $iVar = 0 ; This variable in local scope will be changed.

    For $i = 1 To 10
        $iVar += 1
    Next
    MsgBox($MB_SYSTEMMODAL, '$iVar=' & $iVar, $sMessage)
EndFunc   ;==>Example

Invoke an Au3Check error.

#include <Constants.au3>

Example()

Func Example()
    Local Const $sMessage = 'Some message that is assigned to a variable which won''t be changed i.e. constant variable.' ; This won't change
    Local $iVar = 0 ; This variable in local scope will be changed.

    ; Creates an error as previously being declared as a Const.
    $sMessage = ''

    For $i = 1 To 10
        $iVar += 1
    Next
    MsgBox($MB_SYSTEMMODAL, '$iVar=' & $iVar, $sMessage)
EndFunc   ;==>Example

Edited February 1, 2013 by guinness

[BrewManNH]

I use the Const keyword for handle and control ID variables so I don't accidentally include something that changes it later. I started doing this when I used the same variable name for a label I was using as a timer, and didn't use good naming techniques and then I had the same name in an include file that changed it. Now that I name my variables differently, I don't ever see this issue, but still use the Const keyword for the handles because they should never be changed, and this assures it.

[guinness]

I should have mentioned I use AutoIt-hungarian-like notation for variable naming. Yes, I made that name up!

It must have been a Global you were using BrewManNH?

Edited February 1, 2013 by guinness

[Melba23]

guinness,

I have just looked through some of my scripts and, rather to my surprise, I find I use it very sparingly:

; IDs of icons stared within the compiled exe
Global Const $iPlay_Icon = -5, $iPause_Icon = -13, $iIndex_Icon = -21, $iFile_Icon = -22, $iList_Icon = -23

; Basic colours to ensure consistency in the script
Global Const $iRed = 0xFF8888, $iAmber = 0xFFCC88, $iYellow = 0xFFFF88, $iBlue = 0x80FFFF
Global Const $iGrey = 0xCCCCCC, $iGreen = 0xCCFFCC, $iWhite = 0xFFFFFF, $iBlack = 0

M23

[BrewManNH]

It was a handle to a control, and it was a global because it was meant to be a global.

[guinness]

It was a handle to a control, and it was a global because it was meant to be a global.

I'm not judging -_0 If I need to manipulate Global variables in custom UDFs I create wrapper functions to get/set them. An idea I adopted from Valik.

Note: Can't find the post between him and MvGulik about this.Found it >>

I have just looked through some of my scripts and, rather to my surprise, I find I use it very sparingly:

I will spend the rest of my free time today creating a parser to check whether or not a variable should be a constant. Therefore I will take a break from the Forum today! Edited February 1, 2013 by guinness

[guinness]

I eventually created a very very rough parser to determine if a variable was to be declared as Const or not.

[kylomas]

guinness,

Based on the rule "if it is assigned a value and never changed"?

Parsers are interesting to me. If there is anything I can do to help, please let me know.

kylomas

[guinness]

I'm always open to ideas and suggestions kylomas.

[Shaggi]

Well i guess it doesn't really matter that much in interpreted/dynamic languages, besides compile-time checking of assignment to constant variables (does autoitcheck do this?). It's useful to avoid name clashing and give symbolic meaning / clues to what a variable does. Also, of course, it should be used on constants, which autoit, to my understanding, is able to optimize.

In compiled languages, if you explicitly state the constness of variables (and the compiler can guarantee this), the compiler is able to do a lot of optimizations on code, registers, memory layouts, copying (specifically able to do reference passing instead of copying parameters) etc.

I do think it's an excellent coding practice in dynamic languages though, to make everything you don't intend to change immutable, both because of symbolism but also transitions to/from other languages.

[guinness]

As I've understood from trancexx, AutoIt just marks in the variable table whether or not the variable is a constant, no optimisation (though I could be wrong not being a Dev and all.) Au3Check will throw errors if you assign a variable with the Const keyword, thus less likely to have issue(s) as BrewManNH did.

I agree with your last statement.

Edited February 2, 2013 by guinness

[czardas]

I would imagine that using Const is useful when working alongside other coders or if someone else decides to update or modify your code. This way they will be less likely to make a mistake. I would always use Const to declare a mathematical constant, or any variable used as some kind of standardized unit calibration or ratio. Pi would fall into this category.

Regarding other uses, I'm not really sure if you can give a clear set of rules, since it can be applied in so many different situations. I'm also not sure about handles, since I don't know if Windows will reassign the same handle to another control under certain circumstances. Then again. perhaps that's just me being paranoid.

I don't think the keyword should be used willy nilly. Of course it makes sense to use it for things like Windows control styles (already defined as constants) etc...

Edited February 2, 2013 by czardas

[guinness]

I don't think you have to worry about that.

[czardas]

I don't think you have to worry about that.

Are you refering to control handles free to be reassigned after you destroy the original controls? I thought Windows might do something like that. If I destroy a control and then recreate it, it doesn't always get the same handle, if I remember correctly from past experience.

Edited February 2, 2013 by czardas

[guinness]

Are you refering to control handles free to be reassigned after you destroy the original controls? I thought Windows might do something like that. If I destroy a control and then recreate it, it doesn't get the same handle, if I remember correctly from past experience.

OK, now I get it. Then you would of course declare wit the same variable which Au3Check would throw an error if assigned with the Const keyword. Edited February 2, 2013 by guinness

[czardas]

I think so.

[jchd]

For what it is worth, I've often made fair use of the Enum keyword as well as Const. That you use/need auto_incrementing successive values or forced ones, I find an Enum group cleaner than a series of separate Const as it more clearly shows the common character between identificators listed. Yet the distinction is essentially cosmetic (for now).

[guinness]

Enum with arrays is something I have been using for about 6 months now and even though it adds nothing in terms of enhancement, it does help with readability and not having to worry about modifying index values.

[jchd]

Yeah, typical use.

[guinness]

You know when you 'hack' something together because you need it right away, that's exactly what I did the other day with my 'is it a constant variable' script. So today I will improve on this and may post to the Forum, depending on how well structured it is.