Do I have to export all variables and functions from my PM file?

SergioQ has asked for the wisdom of the Perl Monks concerning the following question:

My Perl PM has the following lines of code:

our @itemsArray = qw( sheet_no sheet_name item );
our $itemsArraySize = @itemsArray;
our @itemRecords;

our @ISA = qw(Exporter);
our @EXPORT = qw(    getTopHTML
                    getBottomHTML
                    ssPrintTable
                    $domainname
                    msgInTable
                    LogInToDB
                    LogOutOfDB
                    createRandonNumber
                    createRawDB
                    printLine
                    alertSupport
                    insertItem
                    getRecords
);
[download]

And I've wondered if I must export functions, strings, arrays, etc. etc. that are not used ouside of the PM module? Obviously I have already played with it both ways, and I have had no headaches. But that doesn't mean it's the proper way.

So that's my question: If I don't use a specific variable outside the PM itself, do I need to export it?

That includes an array, which the PM might return an array reference to the calling perl script. My limited knowledge of Perl recalls that Perl knows if a variable is still in use and will keep it alive if necessary, but again, I learned only as much Perl as I needed to get some very limited scripts written.

Thank you

Comment on Do I have to export all variables and functions from my PM file? Download Code

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Re: Do I have to export all variables and functions from my PM file? by afoken (Chancellor) on Mar 05, 2022 at 21:20 UTC
So, you have triggered one of my pet problems: Inheriting from Exporter. `our @ISA = qw(Exporter);` [download] You don't have to inherit from Exporter. In fact, you shouldn't (at least in my oppinion), even if it currently does not hurt most times. See also Re: Adding "sub import{}" to my module makes global symbols require an explicit package name, Re: Advice on style, Re: How to create a reusable module with Exporter [SOLVED]. The Exporter documentation wasn't really that great in this regard. It has become better, but it still suggests inheriting in the very first example. See also Re^2: Advice on style, Re^4: Advice on style, Re^2: Exporter in an OO module?, Re^2: Exporter. Correct way to override import?. What you should do is documented in Exporting-Without-Inheriting-from-Exporter of Exporter: `use Exporter qw( import );` [download] And that's it. No need to mess with `@ISA`, base, or parent, unless you need to support old perls from almost two decades ago (`Exporter` older than 5.57, i.e. perl older than 5.8.3). Alexander -- Today I will gladly share my knowledge and experience, for there are no sweeter words than "I told you so". ;-)	[reply] [d/l] [select]
Re: Do I have to export all variables and functions from my PM file? by LanX (Saint) on Mar 05, 2022 at 20:21 UTC
> So that's my question: If I don't use a specific variable outside the PM itself, do I need to export it? No, to the contrary: You shouldn't because you are needlessly polluting the namespace. Furthermore it's normally better not to export on default, but to populate `@EXPORT_OK` instead. And exporting variables is considered bad practice, only export subs. Cheers Rolf _{(addicted to the Perl Programming Language :) Wikisyntax for the Monastery}	[reply] [d/l]
Re^2: Do I have to export all variables and functions from my PM file? by eyepopslikeamosquito (Archbishop) on Mar 06, 2022 at 02:27 UTC
For some background on the principles behind the LanX's excellent points, see Information hiding -- the general idea is to hide your module's implementation (which is likely to change over time) from the (possibly many) programs that call it. So don't just blindly export all your module's variables! Instead, think harder about designing a good module interface, one that will stand the test of time, and so allow you to make many future module improvements without needing to update in step all your programs that use it. This topic is discussed in much more detail at: On Interfaces and APIs	[reply]
Re^3: Do I have to export all variables and functions from my PM file? by cavac (Prior) on Mar 09, 2022 at 14:30 UTC
As long as you don't make it too hard to modify the behaviour of your code, that is. Also see the discussion on How to redefine a modules private function?. `perl -e 'use Crypt::Digest::SHA256 qw[sha256_hex]; print substr(sha256_hex("the Answer To Life, The Universe And Everything"), 6, 2), "\n";'`	[reply] [d/l]
Re^4: Do I have to export all variables and functions from my PM file? by eyepopslikeamosquito (Archbishop) on Mar 11, 2022 at 00:14 UTC
Re^5: Do I have to export all variables and functions from my PM file? by cavac (Prior) on Mar 11, 2022 at 15:37 UTC
Re^4: Do I have to export all variables and functions from my PM file? by eyepopslikeamosquito (Archbishop) on Mar 10, 2022 at 02:05 UTC
Re^2: Do I have to export all variables and functions from my PM file? by Anonymous Monk on Mar 07, 2022 at 15:33 UTC
In fact, it is probably better to make the variables lexical (i.e. 'my' rather than 'our'). The 'our' variables are still accessible using their fully-qualified names. The 'my' variables are not accessible at all from outside the scope that declares them, unless some code in that scope passes them out.	[reply]
Re^3: Do I have to export all variables and functions from my PM file? by LanX (Saint) on Mar 07, 2022 at 15:51 UTC
Yes, in general one is better off to always default to private vars with `my` only use public `our` when really needed But this is not always so, there are always exceptions to the rule. Some modules use package vars for external config, e.g. Text::Glob or Data::Dumper ° Some even export readonly vars to be used as constants (instead of barewords without sigils) Cheers Rolf _{(addicted to the Perl Programming Language :) Wikisyntax for the Monastery} °) of course TIMTOWTDI, these design patterns date back to the Perl4 times, which had neither OOP nor private lexical vars. Data::Dumper for instance has a dual API.	[reply] [d/l] [select]
Re^3: Do I have to export all variables and functions from my PM file? by Anonymous Monk on Mar 08, 2022 at 10:15 UTC
The 'my' variables are not accessible at all from outside the scope that declares them, unless some code in that scope passes them out. PadWalker	[reply]
Re: Do I have to export all variables and functions from my PM file? by stevieb (Canon) on Mar 06, 2022 at 02:42 UTC
If I don't use a specific variable outside the PM itself, do I need to export it? No. In fact, please don't export variables at all. Use functions that access the variables, and export them instead. To further, the names you're using lead me to believe that this is a good candidate for an Object Oriented module, therefore you won't have to export anything at all, plus you'll get the added benefit of being able to keep state within your objects.	[reply]
Re: Do I have to export all variables and functions from my PM file? by syphilis (Archbishop) on Mar 05, 2022 at 23:55 UTC
And I've wondered if I must export functions, strings, arrays, etc. etc. that are not used outside of the PM module? I just want to point out that (as you may already know) functions, package variables and package constants can all be accessed from the "outside" even if they're not exported. They just have to be accessed via their fully qualified names - eg `My::Mod::foo()` instead of simply `foo()`, `$My::Mod::package_var` instead of `$package_var` and `My::Mod::CONST_VAL` instead of `CONST_VAL`. Cheers, Rob	[reply] [d/l] [select]