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

       Damian Conway  "<DCONWAY@cpan.org>"

       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>.

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

       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.

       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.

       "%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.

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       WITH ANY OTHER SOFTWARE), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF  SUCH
       DAMAGES.

perl v5.34.0                                       2022-06-11                             Class::Std::Utils(3pm)

       None reported.

       "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":

               Thesubroutineisalwayscalledwiththeoriginalmulti-levelargumenthashfromtheconstructor.Itthenlooksuptheclass'sownname(i.e.its"caller"package)intheargumenthash,toseeifaninitializerwiththatkeyhasbeendefined.Finally,"extract_initializers_for()"returnstheflattenedsetofkey/valuepairsfortheclass'sinitializerset,byappendingtheclass-specificinitializersubhashtotheendoftheoriginalgenericinitializerhash.Appendingthespecificinitializersafterthegenericonesmeansthatanykeyintheclass-specificsetwilloverrideanykeyinthegenericset,therebyensuringthatthemostrelevantinitializersarealwaysselected,butthatgenericinitializersarestillavailablewherenoclass-specificvaluehasbeenpassedin.

           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.

       Copyright (c) 2005, Damian Conway "<DCONWAY@cpan.org>". All rights reserved.

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

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

       The "Class::Std" module

       "Perl Best Practices", O'Reilly, 2005.

           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);

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