# NAME Const::Exporter - Declare constants for export. # VERSION version v1.2.3 # SYNOPSIS Define a constants module: ```perl package MyApp::Constants; 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/ foo $bar /]; # exported by default ``` and use that module: ```perl package MyApp; use MyApp::Constants qw/ $zoo :tag_a /; ... ``` ## Dynamically Creating Constants You may also import a predefined hash of constants for exporting dynamically: ```perl use Const::Exporter; my %myconstants = ( 'foo' => 1, '$bar' => 2, '@baz' => [qw/ a b c /], '%bo' => { a => 1 }, ); # ... do stuff Const::Exporter->import( constants => [%myconstants], # define constants for exporting default => [ keys %myconstants ], # export everything in %myconstants by default ); ``` # DESCRIPTION This module allows you to declare constants that can be exported to other modules. To declare constants, simply group then into export tags: ```perl package MyApp::Constants; use Const::Exporter 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.) If you do give a value, [Const::Exporter](https://metacpan.org/pod/Const%3A%3AExporter) will assume it's another symbol. Your module can include multiple calls to `use Const::Exporter`, so that you can reference constants in other expressions, e.g. ```perl use Const::Exporter tag => [ '$zero' => 0, ]; use Const::Exporter tag => [ '$one' => 1 + $zero, ]; ``` or even something more complex: ```perl use Const::Exporter http_ports => [ 'HTTP' => 80, 'HTTP_ALT' => 8080, 'HTTPS' => 443, ]; use Const::Exporter http_ports => [ '@HTTP_PORTS' => [ HTTP, HTTP_ALT, HTTPS ], ]; ``` Constants can include traditional [constant](https://metacpan.org/pod/constant) symbols, as well as scalars, arrays or hashes. Constants can include values defined elsewhere in the code, e.g. ```perl our $foo; BEGIN { $foo = calculate_value_for_constant(); } use Const::Exporter tag => [ '$foo' ]; ``` Note that this will make the symbol read-only. You don't need to explicitly declare it as such. Enumerated constants are also supported: ```perl use Const::Exporter tag => [ [qw/ foo bar baz /] => 1, ]; ``` will define the symbols `foo` (1), `bar` (2) and `baz` (3). You can also specify a list of numbers, if you want to skip values: ```perl use Const::Exporter tag => [ [qw/ foo bar baz /] => [1, 4], ]; ``` will define the symbols `foo` (1), `bar` (4) and `baz` (5). You can even specify string values: ```perl use Const::Exporter tag => [ [qw/ foo bar baz /] => [qw/ feh meh neh /], ]; ``` however, this is equivalent to ```perl use Const::Exporter tag => [ 'foo' => 'feh', 'bar' => 'meh', 'baz' => 'neh', ]; ``` Objects are also supported, ```perl use Const::Exporter tag => [ '$foo' => Something->new( 123 ), ]; ``` ## Export Tags By default, all symbols are exportable (in `@EXPORT_OK`.) The `:default` tag is the same as not specifying any exports. The `:all` tag exports all symbols. # KNOWN ISSUES ## Support for older Perl versions This module requires Perl v5.10 or newer. Pull requests to support older versions of Perl are welcome. See ["SOURCE"](#source). ## Exporting Functions [Const::Exporter](https://metacpan.org/pod/Const%3A%3AExporter) is not intended for use with modules that also export functions. There are workarounds that you can use, such as getting [Const::Exporter](https://metacpan.org/pod/Const%3A%3AExporter) to export your functions, or munging `@EXPORT` etc. separately, but these are not supported and changes in the future my break our code. ## Mixing POD with Tags The following code is a syntax error, at least with some versions of Perl: ```perl use Const::Exporter =head2 a =cut a => [ foo => 1 ], =head2 b =cut b => [ bar => 2 ]; ``` If you want to mix POD with your declarations, use multiple use lines, e.g. ```perl =head2 a =cut use Const::Exporter a => [ foo => 1 ]; =head2 b =cut use Const::Exporter b => [ bar => 2 ]; ``` # SUPPORT FOR OLDER PERL VERSIONS This module requires Perl v5.10.1 or later. Future releases may only support Perl versions released in the last ten years. # SEE ALSO See [Exporter](https://metacpan.org/pod/Exporter) for a discussion of export tags. ## Similar Modules - [Exporter::Constants](https://metacpan.org/pod/Exporter%3A%3AConstants) This module only allows you to declare function symbol constants, akin to the [constant](https://metacpan.org/pod/constant) module, without tags. - [Constant::Exporter](https://metacpan.org/pod/Constant%3A%3AExporter) This module only allows you to declare function symbol constants, akin to the [constant](https://metacpan.org/pod/constant) module, although you can specify tags. - [Constant::Export::Lazy](https://metacpan.org/pod/Constant%3A%3AExport%3A%3ALazy) This module only allows you to declare function symbol constants, akin to the [constant](https://metacpan.org/pod/constant) module by defining functions that are only called as needed. The interface is rather complex. - [Const::Fast::Exporter](https://metacpan.org/pod/Const%3A%3AFast%3A%3AExporter) This module will export all constants declared in the package's namespace. # SOURCE The development version is on github at [https://github.com/robrwo/Const-Exporter](https://github.com/robrwo/Const-Exporter) and may be cloned from [git://github.com/robrwo/Const-Exporter.git](git://github.com/robrwo/Const-Exporter.git) # BUGS Please report any bugs or feature requests on the bugtracker website [https://github.com/robrwo/Const-Exporter/issues](https://github.com/robrwo/Const-Exporter/issues) When submitting a bug or request, please include a test-file or a patch to an existing test-file that illustrates the bug or desired feature. # AUTHOR Robert Rothenberg <rrwo@cpan.org> # CONTRIBUTORS - Slaven Rezić <slaven@rezic.de> - B. Estrade <estrabd@cpan.org> # COPYRIGHT AND LICENSE This software is Copyright (c) 2014-2023 by Robert Rothenberg. This is free software, licensed under: ``` The Artistic License 2.0 (GPL Compatible) ```