NAME

Const::Exporter - export constants

SYNOPSIS

Define a constants module:

  package MyApp::Constants;

  use Const::Fast;

  const our $zoo => 1234;

  use Const::Exporter

     tag_a => [                  # use MyApp::Constants /:tag_a/;
        'foo'  => 1,             # exports "foo"
        '$bar' => 2,             # exports "$bar"
        '@baz' => [qw/ a b c /], # exports "@baz"
        '%bo'  => { a => 1 },    # exports "%bo"
     ],

     tag_b => [                  # use MyApp::Constants /:tag_b/;
        'foo',                   # exports "foo" (same as from ":tag_a")
        '$zoo',                  # exports "$zoo" (as defined above)
     ];

  # `use Const::Exporter` can be specified multiple times

  use Const::Exporter

     tag_b => [                 # we can add symbols to ":tab_b"
        'moo' => $bar,          # exports "moo" (same value as "$bar")
     ],

     enums => [

       [qw/ goo gab gub /] => 0, # exports enumerated symbols, from 0..2

     ],

     default => [qw/ fo $bar /]; # exported by default

and use that module:

  package MyApp;

  use MyApp::Constants qw/ $zoo :tag_a /;

  ...

DESCRIPTION

This module allows you to declare constants that can be exported to other modules.

To declare constants, simply group then into export tags:

  package MyApp::Constants;

  use Const::Exporer

    tag_a => [
       'foo' => 1,
       'bar' => 2,
    ],

    tag_b => [
       'baz' => 3,
       'bar',
    ],

    default => [
       'foo',
    ];

Constants in the "default" tag are exported by default (that is, they are added to the @EXPORTS array).

When a constant is already defined in a previous tag, then no value is specified for it. (For example, "bar" in "tab_b" above.)

Your module can include multiple calls to use Const::Exporter, so that you can reference constants in other expressions, e.g.

  use Const::Exporter

    tag => [
        '$zero' => 0,
    ];

  use Const::Exporter

    tag => [
        '$one' => 1 + $zero,
    ];

Constants can include traditional constant symbols, as well as scalars, arrays or hashes.

Constants can include values defined elsewhere in the code, e.g.

  our $foo;

  BEGIN {
     $foo = calculate_value_for_constant();
  }

  use Const::Exporer

    tag => [ '$foo' ];

Note that this will make the symbol read-only. You don't need to explicitly declare it as such.

SEE ALSO

See Exporter for a discussion of export tags.

Similar Modules

Exporter::Constants

Constant::Exporter

Constant::Exporter::Lazy

Modules for Declaring Readonly values

constant

Readonly

Const::Fast

AUTHOR

Robert Rothenberg, <rrwo at cpan.org>

LICENSE AND COPYRIGHT

Copyright 2014 Robert Rothenberg.

This program is free software; you can redistribute it and/or modify it under the terms of the the Artistic License (2.0). You may obtain a copy of the full license at:

http://www.perlfoundation.org/artistic_license_2_0

Any use, modification, and distribution of the Standard or Modified Versions is governed by this Artistic License. By using, modifying or distributing the Package, you accept this license. Do not use, modify, or distribute the Package, if you do not accept this license.

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This license includes the non-exclusive, worldwide, free-of-charge patent license to make, have made, use, offer to sell, sell, import and otherwise transfer the Package with respect to any patent claims licensable by the Copyright Holder that are necessarily infringed by the Package. If you institute patent litigation (including a cross-claim or counterclaim) against any party alleging that the Package constitutes direct or contributory patent infringement, then this Artistic License to you shall terminate on the date that such litigation is filed.

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