NAME

Class::Std::Utils - Utility subroutines for building "inside-out" objects

VERSION

This document describes Class::Std::Utils version 0.0.3

SYNOPSIS

    use Class::Std::Utils;

    # Constructor for anonymous scalars...
    my $new_object = bless anon_scalar(), $class;

    # Convert an object reference into a unique ID number...
    my $ID_num = ident $new_object;

    # Extract class-specific arguments from a hash reference...
    my %args = extract_initializers_from($arg_ref);

DESCRIPTION

This module provides three utility subroutines that simplify the creation of "inside-out" classes. See Chapters 15 and 16 of "Perl Best Practices" (O'Reilly, 2005) for details.

INTERFACE

"anon_scalar()"

This subroutine is always exported. It takes no arguments and returns a reference to an anonymous scalar, suitable for blessing as an object.

"ident()"

This subroutine is always exported. It takes one argument--a reference-- and acts exactly like the "Scalar::Util::refaddr()", returning a unique integer value suitable for identifying the referent.

"extract_initializers_from()"

This subroutine is always exported. It takes one argument--a hash reference-- and returns a "flattened" set of key/value pairs extracted from that hash.

The typical usage is:

    my %class_specific_args = extract_initializers_from($args_ref);

The argument hash is flattened as described in Chapter 16 of "Perl Best Practices":

The subroutine is always called with the original multi-level argument hash from the constructor. It then looks up the class's own name (i.e. its "caller" package) in the argument hash, to see if an initializer with that key has been defined. Finally, "extract_initializers_for()" returns the flattened set of key/value pairs for the class's initializer set, by appending the class-specific initializer subhash to the end of the original generic initializer hash. Appending the specific initializers after the generic ones means that any key in the class- specific set will override any key in the generic set, thereby ensuring that the most relevant initializers are always selected, but that generic initializers are still available where no class-specific value has been passed in.

In other words, given:

    my $arg_ref = {
        key_1 => 'generic value 1',
        key_2 => 'generic value 2',

        'Base::Class' => {
            key_1 => 'base value 1'
        },

        'Der::Class' => {
            key_1 => 'der value 1'
            key_2 => 'der value 2'
        },
    };

    package Base::Class;
    use Class::Std::Utils;

    my %base_args = extract_initializers_from($arg_ref);

    package Der::Class;
    use Class::Std::Utils;

    my %der_args = extract_initializers_from($arg_ref);

then %base_args would be initialized to:

    (
        key_1 => 'base value 1',
        key_2 => 'generic value 2',

        'Base::Class' => {
            key_1 => 'base value 1',
        },

        'Der::Class' => {
            key_1 => 'der value 1',
            key_2 => 'der value 2',
        },
    )

whilst %der_args would be initialized to:

    (
        key_1 => 'der value 1',
        key_2 => 'der value 2',

        'Base::Class' => {
            key_1 => 'base value 1',
        },

        'Der::Class' => {
            key_1 => 'der value 1',
            key_2 => 'der value 2',
        },
    )

That is, the top-level entries would be replaced by any second-level entries with the same key that appear in a top-level entry of the same name as the calling package.

This means that each class can just refer to $args{key_1} and $args{key_2} and be confident that the resulting values will be the most specific available for that class.

DIAGNOSTICS

"%s initializer must be a nested hash": Thrown by "extract_initializers_from()". You specified a top-level key that has the same name of the current class, but the value of that key wasn't a hash reference.

CONFIGURATION AND ENVIRONMENT

Class::Std::Utils requires no configuration files or environment variables.

DEPENDENCIES

Thsi module requires both the "Scalar::Util" and "List::Util" modules, which are standard in Perl 5.8 and available from the CPAN for earlier versions of Perl.

INCOMPATIBILITIES

None reported.

BUGS AND LIMITATIONS

No bugs have been reported.

Please report any bugs or feature requests to "bug-class-std-utils@rt.cpan.org", or through the web interface at <http://rt.cpan.org>.

AUTHOR

Damian Conway "<DCONWAY@cpan.org>"

LICENCE AND COPYRIGHT

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

DISCLAIMER OF WARRANTY

BECAUSE THIS SOFTWARE IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR THE SOFTWARE, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE SOFTWARE "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE SOFTWARE IS WITH YOU. SHOULD THE SOFTWARE PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR, OR CORRECTION.

IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR REDISTRIBUTE THE SOFTWARE AS PERMITTED BY THE ABOVE LICENCE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE SOFTWARE (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE SOFTWARE TO OPERATE WITH ANY OTHER SOFTWARE), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.