NAME
define - Perl pragma to declare global constants
SYNOPSIS
#--- in package/file main ---#
package main;
# the most frequenly used application of this pragma
use define DEBUG => 0;
# define a constant list
use define DWARVES => qw(happy sneezy grumpy);
# define several at a time via a hashref list, like constant.pm
use define {
FOO => 1,
BAR => 2,
BAZ => 3,
};
use Some::Module;
use My::Module;
#--- in package/file Some::Module ---#
package Some::Module
no define DEBUG =>;
no define DWARVES =>;
# define a master object that any package can import
sub new { ... }
use define OBJECT => __PACKAGE__->new;
# if DEBUG is false, the following statement isn't even compiled
warn "debugging stuff here" if DEBUG;
my $title = "Snow white and the " . scalar DWARVES . " dwarves";
#--- in package/file My::Module ---#
package My::Module
no define;
warn "I prefer these dwarves: " join " ", DWARVES if DEBUG;
OBJECT->method(DWARVES);DESCRIPTION
Use this pragma to define global constants.
USAGE
Defining constants
Global constants are defined through the same calling conventions as constant.pm:
use define FOO => 3;
use define BAR => ( 1, 2, 3 );
use define {
BAZ => 'dogs',
QUX => 'cats',
};Importing constants by name
To use a global constant, you import it into your package as follows:
no define FOO =>;If FOO has been defined, it gets set to its defined value, otherwise it is set to undef. Note that the reason for the '=>' operator here is to parse FOO as a string literal rather than a bareword (you could also do no define 'FOO').
Importing constants willy-nilly
To import ALL defined constants into your package, you can do the following:
no define;This is quick, but messy, as you can't predict what symbols may clash with those in your package's namespace.
NOTES
See constant. Most of the same caveats apply here.
Your code should be arranged so that any no define statements are executed after the use define statement for a given symbol. If the order is reversed, a warning will be emitted.
As a rule, modules shouldn't be defining global constants; they should import constants defined by the main body of your program.
If a module does define a global constant (eg. a master object), the module should be use'd before any other modules (or lines of code) that refer to the constant.
If you define the same symbol more than once, a warning will be emitted.
SEE ALSO
constant - core module for defining constants in the same way as this module.
Const::Fast - CPAN module for defining immutable variables (scalars, hashes, and arrays).
constant modules - a review of CPAN modules for defining constants.
REPOSITORY
https://github.com/neilb/define
AUTHOR
Gary Gurevich (garygurevich at gmail)COPYRIGHT AND LICENSE
Copyright (C) 2004 by Gary Gurevich
This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.