/ 
constant-our-0.05
River stage zero No dependents
/ constant::our

NAME

constant::our - Perl pragma to declare constants like our vars

VERSION

Version 0.05

SYNOPSIS

use constant::our { DEBUG => 1 };
use constant::our {
    DEBUG_SQL => 1,
    DEBUG_CACHE => 1,
    };

######################
package My::Cool::Tools;
use constant::our qw(DEBUG DEBUG_SQL);

if(DEBUG)
{
    warn "DEBUG: $debug_info";
    if(DEBUG_SQL)
    {
        warn "DEBUG_SQL: $querty";
    }
}

# or
DEBUG && warn "DEBUG: $debug_info";
DEBUG && DEBUG_SQL && warn "DEBUG_SQL: $querty";

# Environment
$ export CONSTANT_OUR_DEBUG=1
$ perl -e'use constant::our qw(DEBUG); DEBUG && {warn "Running in debug mode"}'

DESCRIPTION

This pragma extends standard pragma 'constant'.

As you may know, when a constant is used in an expression, Perl replaces it with its value at compile time, and may then optimize the expression further.

You can inspect this behavior by yourself:

$ perl -MO=Deparse -e'use constant{DEBUG => 1}; warn "1"; if(DEBUG){warn "2"} warn "3";'
use constant ({'DEBUG', 1});
warn '1';
do {
    warn '2'
};
warn '3';

All warns are here.

$ perl -MO=Deparse -e'use constant{DEBUG => 0}; warn "1"; if(DEBUG){warn "2"} warn "3";'
use constant ({'DEBUG', 0});
warn '1';
'???';
warn '3';

Notice the '???' instead of the second 'warn'.

So you can do something like this:

# in the main script
use constant DEBUG => 0;

# in a module
if(main::DEBUG)
{
    # some debug code goes here
}

But you should declare all constants you use, you can't simply write

if (main::DEBUG_SQL)
{
}

without corresponding

use constant DEBUG_SQL => 0;

in the main script.

With constant::our you can freely use "undeclared" constants in your condition statements.

# main script
use constant::our {
    DEBUG => 1,
    DEBUG_CACHE => 1,
    };

######################
package My::Cool::Tools;
use constant::our qw(DEBUG DEBUG_SQL); # don't need DEBUG_CACHE, but want (undeclared) DEBUG_SQL

DEBUG && warn "DEBUG: $debug_info";              # DEBUG --> 1
DEBUG && DEBUG_SQL && warn "DEBUG_SQL: $query";  # DEBUG_SQL --> undef

stderr:
"DEBUG: ..."

IMPORTANT

A constant should be declared no more than one time. If you try to declare a constant twice (with different values), your program will die.

Since use of undeclared constant implicitly declares it, you should declare your constants _before_ you start use them.

EXPORT

Nothing by default.

SEE ALSO

constant

constant::abs && constant::def

THANKS

Bolshakova Elena

Neil Bowers

AUTHOR

Green, <Evdokimov.Denis at gmail.com>

BUGS

Please report any bugs or feature requests to bug-constant-our at rt.cpan.org, or through the web interface at http://rt.cpan.org/NoAuth/ReportBug.html?Queue=constant::our. I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.

SUPPORT

You can find documentation for this module with the perldoc command.

perldoc constant::our

You can also look for information at:

COPYRIGHT & LICENSE

Copyright 2009 Green, all rights reserved.

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.