constant::our
This pragma extends standard pragma 'constant'.

INSTALLATION

To install this module, run the following commands:

    perl Build.PL
    ./Build
    ./Build test
    ./Build install

DESCRIPTION

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: ..."

SUPPORT AND DOCUMENTATION

After installing, you can find documentation for this module with the
perldoc command.

    perldoc constant::our

You can also look for information at:

    RT, CPAN's request tracker
        http://rt.cpan.org/NoAuth/Bugs.html?Dist=constant::our

    AnnoCPAN, Annotated CPAN documentation
        http://annocpan.org/dist/constant::our

    CPAN Ratings
        http://cpanratings.perl.org/d/constant::our

    Search CPAN
        http://search.cpan.org/dist/constant::our


COPYRIGHT AND LICENCE

Copyright (C) 2009 Green

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