in reply to Is "use" same as include?

I've seen this question before. I'm going to give the same answer (3) None of the above...use a simple DB like a .INI file for this if there a bunch of them. As I said before, you can make a very thin layer for the MyConstants.pm module.

Having said that, alarm bells go off in my brain as to how many of these constants do you have? 10,50,100?

The reason that I'm asking is that in C, a lot of of these #define things have to do with a) memory limits (like array bounds..MAX_LINE_BYTES, etc) or b) stuff like thing "3" in this array means "name". Using Perl constants for either a or b is not the right Perl way.

So anyway, say you have a dozen of these things....the below code will do it. The code in your modules would look like use MyConstants(VAR1 VAR3); I LOVE C, but this is not C. You don't have to import any variable into your name space that you don't need. In C there will be hundreds if not thousands of vars imported into your compile name space via the .h files! In Perl, you can specify which vars you want to import, below this is specified by @EXPORT_OK. If you want all of them, then put them in the @EXPORT list (the default export/import list). Also, in Perl there is really no such thing as a truly "private variable". Even if VAR3 is not exported, it can still be accessed via $MyConstants::VAR3, assuming that $VAR3 has package scope which is what "our" does.

Anyway the below scheme should work fine for like a dozen vars. 

#file MyConstants.pm

use strict;
use warnings;
package MyConstants;
use vars qw(@ISA @EXPORT @EXPORT_OK %EXPORT_TAGS $VERSION);
use Exporter;
our $VERSION=0.1;
our @ISA = qw(Exporter);
our @EXPORT = qw();                  #default export 
our @EXPORT_OK = qw(VAR1 VAR2 VAR3); #by request export

our $VAR1 ="something";
our $VAR2 ="something_else";
our $VAR3 ="something_way_else";

1;

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Update:
I just read the ikegami post and it is completely correct as usual! Perl is not a "lightweight" language. I tried in my code to do something similar to what you would expect with a C .h file. I did not worry about whether some var is truly "constant" or not. I assume that you won't give these vars names or use them in a way that you wouldn't in a C program. Anyway "use MyConstants(VAR1); is most assuredly NOT the same as #include MyConstants.h

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Re^2: Is "use" same as include?
by Anonymous Monk on Jul 15, 2009 at 20:08 UTC
    Thank you folks.

    To answer some question in reply
    a) I have about 500 some constants
    b) Yes the plan was to use these constants for "stuff like thing "3" in this array means "name".
    This is not the right approach for that?
    c) Yes I am currently using the Exporter for this. Here is the code (The recipe to export all symbols is a modified version of a reply that I came across in a different post here at perlmonk) 
    package MyConstants;
require Exporter;
@ISA = qw(Exporter);
our @EXPORT = do {
                    no strict 'refs';
                    keys %{ __PACKAGE__ . '::'};
                 };

use constant VAR1 => VAL1;
use constant VAR2 => VAL2;
#--- 500 more of these
1;

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    Each of the other modules module1.pm, module2.pm, module3.pm then have 
    use MyConstants;

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[d/l]
[select]
      If you intend to export 500 things, then I would argue that there is something fundamentally wrong with the design.

      As what I would call a "sanity check", go look at some HUGE Perl modules. Some of these things have mind-bending, brain-twisting, byzantine complexity, but NONE that I've found have a module that exports 500 things! A dozen? Yeah! Some dozens or even a hundred, maybe! But 500? No!

      Perl has amazing abilities to deal with arrays and complex structures without the use of indicies, without needing a #define statement. Say: 

      @stuff = my($low_temp, $high_temp, $average_temp = split(/\s+/,$line);
+ 
$stuff[0] is $low_temp. 
Do I need a #define LOW_TEMP 0\ /*low_temp var*/$stuff[LOW_TEMP]? NO! 
I just use the variable name that has just been declared: $low_temp.
Forget the idea of $stuff[0] or $stuff[LOW_TEMP].

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      If you could make a short example of why you need so many global variables, it would be helpful because I don't know how to help you further with the data that I have so far.

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[d/l]
      That exports too much. You can't unconditionally export everything that's in the package! Once you fix it, you end up with the code I posted earlier in this thread.
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