Evdokimov Denis > constant-our-0.07 > constant::our

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NAME ^

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

VERSION ^

Version 0.07

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: ..."

ENV ^

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

DEBUGING ^

    use constant::our {CONST => 123};
    use ...
    use ...
    
    use Data::Dumper;
    $Data::Dumper::Sortkeys = 1;
    print Dumper \%constant::our::package_use;
    print Dumper \%constant::our::package_set;
    print Dumper \%constant::our::package_set_implicitly;

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.

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