Const::Exporter - Declare constants for export.
Define a constants module:
package MyApp::Constants; use Const::Fast; 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/ $zoo :tag_a /; ...
This module allows you to declare constants that can be exported to other modules.
To declare constants, simply group then into export tags:
package MyApp::Constants; use Const::Exporter tag_a => [ 'foo' => 1, 'bar' => 2, ], tag_b => [ 'baz' => 3, 'bar', ], default => [ 'foo', ];
Constants in the default tag are exported by default (that is, they are added to the @EXPORTS array).
default
@EXPORTS
When a constant is already defined in a previous tag, then no value is specified for it. (For example, bar in tab_b above.) If you do give a value, Const::Exporter will assume it's another symbol.
bar
tab_b
Your module can include multiple calls to use Const::Exporter, so that you can reference constants in other expressions, e.g.
use Const::Exporter
use Const::Exporter tag => [ '$zero' => 0, ]; use Const::Exporter tag => [ '$one' => 1 + $zero, ];
or even something more complex:
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 symbols, as well as scalars, arrays or hashes.
Constants can include values defined elsewhere in the code, e.g.
our $foo; BEGIN { $foo = calculate_value_for_constant(); } use Const::Exporter tag => [ '$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:
use Const::Exporter tag => [ [qw/ foo bar baz /] => 1, ];
will define the symbols foo (1), bar (2) and baz (3).
foo
baz
You can also specify a list of numbers, if you want to skip values:
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:
use Const::Exporter tag => [ [qw/ foo bar baz /] => [qw/ feh meh neh /], ];
however, this is equivalent to
use Const::Exporter tag => [ 'foo' => 'feh', 'bar' => 'meh', 'baz' => 'neh', ];
Objects are also supported,
use Const::Exporter tag => [ '$foo' => Something->new( 123 ), ];
The following code is a syntax error, at least with some versions of 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.
=head2 a =cut use Const::Exporter a => [ foo => 1 ]; =head2 b =cut use Const::Exporter b => [ bar => 2 ];
By default, all symbols are exportable (in @EXPORT_OK.)
@EXPORT_OK
The :default tag is the same as not specifying any exports.
:default
The :all tag exports all symbols.
:all
Const::Exporter is not intended for use with modules that also export functions.
There are workarounds that you can use, such as getting Const::Exporter to export your functions, or munging @EXPORT etc. separately, but these are not supported and changes in the future my break our code.
@EXPORT
See Exporter for a discussion of export tags.
This module only allows you to declare function symbol constants, akin to the constant module, without tags.
This module only allows you to declare function symbol constants, akin to the constant module, although you can specify tags.
This module only allows you to declare function symbol constants, akin to the constant module by defining functions that are only called as needed. The interface is rather complex.
Robert Rothenberg, <rrwo at cpan.org>
<rrwo at cpan.org>
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:
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To install Const::Exporter, copy and paste the appropriate command in to your terminal.
cpanm
cpanm Const::Exporter
CPAN shell
perl -MCPAN -e shell install Const::Exporter
For more information on module installation, please visit the detailed CPAN module installation guide.