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Keyword-DEVELOPMENT-0.07
River stage zero No dependents
5 ++
/ Keyword::DEVELOPMENT

NAME

Keyword::DEVELOPMENT - Have code blocks which don't exist unless you ask for them.

VERSION

Version 0.06

SYNOPSIS

    use Keyword::DEVELOPMENT;

    sub foo {
        my $self = shift;
        DEVELOPMENT {
            $self->expensive_debugging_code;
        }
        ...
    }

EXPORT

DEVELOPMENT

This module exports one keyword, DEVELOPMENT. This keyword takes a code block.

If the environment variable PERL_KEYWORD_DEVELOPMENT is set to a true value, the code block is executed. Otherwise, the entire block is removed at compile-time, thus ensuring that there is no runtime overhead for the block.

ALternatively, you can set the PERL_KEYWORD_DEVELOPMENT_MATCH variable to a valid Perl regular expression to only run DEVELOPMENT blocks in packages matching the regex.

This is primarily a development tool for performance-critical code.

EXAMPLE

Consider the following code:

    #!/usr/bin/env perl

    BEGIN {
        # just in case someone turned this off
        $ENV{PERL_KEYWORD_DEVELOPMENT} = 1;
    }
    use lib 'lib';
    use Keyword::DEVELOPMENT;

    my $value = 0;
    DEVELOPMENT {
        sleep 10;
        $value = 1;
    }

    print "Our value is $value";

Running this code should print the following after about 10 seconds:

    Our value is 1

However, if you set PERL_KEYWORD_DEVELOPMENT to 0 in the BEGIN block, it prints:

    Our value is 0

To know that we really have no overhead during production, run the code under the debugger with PERL_KEYWORD_DEVELOPMENT set to 0.

    $ perl -d development.pl

    Loading DB routines from perl5db.pl version 1.49_04
    Editor support available.

    Enter h or 'h h' for help, or 'man perldebug' for more help.

    main::(development.pl:10):    my $value = 0;
    auto(-1)  DB<1> {{v
    DB<2> n
    main::(development.pl:10):    my $value = 0;
    auto(-1)  DB<2> v
    7:    use lib 'lib';
    8:    use Keyword::DEVELOPMENT;
    9
    10==>    my $value = 0;

    11     # PERL_KEYWORD_DEVELOPMENT was false, so the development code was removed.
    12     #KDCT:_:_:1 DEVELOPMENT
    13     #line 14 development.pl
    14
    15
    16:    print "Our value is $value";
    DB<2>

As you can see, there are only comments there, no code.

Note the handy line directive on line 13 to ensure your line numbers remain correct. If you're not familiar with line directives, see https://perldoc.perl.org/perlsyn.html#Plain-Old-Comments-(Not!)

PRODUCTION

As an if/else, you use pass -production in the import list and get a PRODUCTION keyword, too. A PRODUCTION block will always fire when a DEVELOPMENT block does not, and vice versa.

    use Test::More;
    use Keyword::DEVELOPMENT '-production';

    my $value = 0;
    DEVELOPMENT {
        $value = 1;
        fail "DEVELOPMENT should be off, so we shouldn't get to here";
    }
    is $value, 0, 'Our DEVELOPMENT function should not be called';

    $value = 0;
    PRODUCTION {
        $value = 1;
        pass "DEVELOPMENT should be off, so PRODUCTION blocks should fire";
    }
    ok $value, '... and be able to alter variables in its scope.';
    done_testing;

MATCHING PACKAGES

If you use Keyword::DEVELOPMENT extensively, you may find that the DEVELOPMENT block is called too frequently. As of version 0.05, an experimental feature has been added to allow you to only invoke DEVELOPMENT blocks in packages matching a regex. Set the PERL_KEYWORD_DEVELOPMENT_MATCH variable to a Perl regular expression instead of the PERL_KEYWORD_DEVELOPMENT variable. Only packages whose names match the regular expression will have their DEVELOPMENT block triggered.

    PERL_KEYWORD_DEVELOPMENT_MATCH='^(?:Our::Codebase::|Our::MonkeyPatches::)' \
        perl some_code.pl

The above will only run DEVELOPMENT for packages whose package names start with Our::Codebase:: or Our::MonkeyPatches::.

ALTERNATIVES

As SawyerX pointed out, can replicate the functionality of this module in pure Perl, if desired:

    use constant PRODUCTION => !!$ENV{PRODUCTION};
    do {expensive_debugging_code()} unless PRODUCTION;

Versus:

    use Keyword::DEVELOPMENT;
    DEVELOPMENT {expensive_debugging_code()};

The first version works because the line is removed entirely from the source code using constant-folding (if PRODUCTION evaluates to false during compile time, the entire line will be omitted).

I think Keyword::DEVELOPMENT is less fragile in that you never need to remember the unless PRODUCTION statement modifier. However, we do rely on the pluggable keyword functionality introduced in 5.012. Be warned!

AUTHOR

Curtis "Ovid" Poe, <ovid at allaroundtheworld.fr>

BUGS AND LIMITATIONS

Please report any bugs or feature requests to bug-keyword-assert at rt.cpan.org, or through the web interface at http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Keyword-DEVELOPMENT. 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 Keyword::DEVELOPMENT

You can also look for information at:

ACKNOWLEDGEMENTS

Thanks to Damian Conway for the excellent Keyword::Declare module.

LICENSE AND COPYRIGHT

Copyright 2017 Curtis "Ovid" Poe.

This program is free software; you can redistribute it and/or modify it under the terms of the the Artistic License (2.0). You may obtain a copy of the full license at:

http://www.perlfoundation.org/artistic_license_2_0

Any use, modification, and distribution of the Standard or Modified Versions is governed by this Artistic License. By using, modifying or distributing the Package, you accept this license. Do not use, modify, or distribute the Package, if you do not accept this license.

If your Modified Version has been derived from a Modified Version made by someone other than you, you are nevertheless required to ensure that your Modified Version complies with the requirements of this license.

This license does not grant you the right to use any trademark, service mark, tradename, or logo of the Copyright Holder.

This license includes the non-exclusive, worldwide, free-of-charge patent license to make, have made, use, offer to sell, sell, import and otherwise transfer the Package with respect to any patent claims licensable by the Copyright Holder that are necessarily infringed by the Package. If you institute patent litigation (including a cross-claim or counterclaim) against any party alleging that the Package constitutes direct or contributory patent infringement, then this Artistic License to you shall terminate on the date that such litigation is filed.

Disclaimer of Warranty: THE PACKAGE IS PROVIDED BY THE COPYRIGHT HOLDER AND CONTRIBUTORS "AS IS' AND WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES. THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, OR NON-INFRINGEMENT ARE DISCLAIMED TO THE EXTENT PERMITTED BY YOUR LOCAL LAW. UNLESS REQUIRED BY LAW, NO COPYRIGHT HOLDER OR CONTRIBUTOR WILL BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, OR CONSEQUENTIAL DAMAGES ARISING IN ANY WAY OUT OF THE USE OF THE PACKAGE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.