in reply to Re: Reading the script code from itself
in thread Reading the script code from itself

Thank you!

What I want to acheive is to have a package full of constants needed by a project. I just want constants to be exportable by tags, but I don't want to indicate constant names twice, as I want to do it only once - when I'm defining those constants.

So, I'd love it to look like that: 

# :tag1
use constant constant1 => 1;
use constant constant2 => 2;
use constant constant3 => 3;
# :tag2
use constant constant4 => 4;
use constant constant5 => 5;
use constant constant6 => 6;
# :tag3
use constant constant4 => 4;
use constant constant5 => 5;
use constant constant6 => 6;

@EXPORT_TAGS = some_cool_internal_subrotine_making_the_hash_of_tags_to
+_be_exported();

[download]

P.S. I'm already using a complicated structure of configuration files in this project, but I want to have constants somewhere in the code where they can't be changed by an user (as configuration files acutally can be changed).

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Re^3: Reading the script code from itself
by Anonymous Monk on May 29, 2014 at 13:24 UTC

    Disclaimer: I find the design questionable... you should consider not using constant (in fact Conway's Perl Best Practices recommends against it, e.g. Perl::Critic::Policy::ValuesAndExpressions::ProhibitConstantPragma) and look at alternatives such as using a locked hash (or even a function) to return your "constant" values.

    As is said, Perl gives you just enough rope to hang yourself with, so here you go:

    package ConstExporter;
use warnings;
use strict;

my %CONSTANTS = (
    foo => "abc",
    bar => "xyz",
    quz => "123",
);

sub import {
    my ($class, @export) = @_;
    my ($callpack) = caller;
    for my $exp (@export) {
        die "bad constant name '$exp'"
            unless exists $CONSTANTS{$exp};
        no strict 'refs';
        *{"${callpack}::$exp"} = sub () { $CONSTANTS{$exp} };
    }
}

1;

    [download]

    Use it in the usual way: use ConstExporter qw/foo bar/;

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      Thank you! :)

      V.Melnik
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