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constant-our-0.01
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NAME

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

VERSION

Version 0.01

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";

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

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.