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.\" ========================================================================
.\"
.IX Title "Class::Std::Utils 3pm"
.TH Class::Std::Utils 3pm "2022-06-11" "perl v5.34.0" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
Class::Std::Utils \- Utility subroutines for building "inside\-out" objects
.SH "VERSION"
.IX Header "VERSION"
This document describes Class::Std::Utils version 0.0.3
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\&    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);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
This module provides three utility subroutines that simplify the creation of
\&\*(L"inside-out\*(R" classes. See Chapters 15 and 16 of \*(L"Perl Best Practices\*(R"
(O'Reilly, 2005) for details.
.SH "INTERFACE"
.IX Header "INTERFACE"
.ie n .IP """anon_scalar()""" 4
.el .IP "\f(CWanon_scalar()\fR" 4
.IX Item "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.
.ie n .IP """ident()""" 4
.el .IP "\f(CWident()\fR" 4
.IX Item "ident()"
This subroutine is always exported. It takes one argument\*(--a reference\*(--
and acts exactly like the \f(CW\*(C`Scalar::Util::refaddr()\*(C'\fR, returning a unique
integer value suitable for identifying the referent.
.ie n .IP """extract_initializers_from()""" 4
.el .IP "\f(CWextract_initializers_from()\fR" 4
.IX Item "extract_initializers_from()"
This subroutine is always exported. It takes one argument\*(--a hash reference\*(--
and returns a \*(L"flattened\*(R" set of key/value pairs extracted from that hash.
.Sp
The typical usage is:
.Sp
.Vb 1
\&    my %class_specific_args = extract_initializers_from($args_ref);
.Ve
.Sp
The argument hash is flattened as described in Chapter 16 of \*(L"Perl Best
Practices\*(R":
.RS 4
.Sp
.RS 4
\&\fIThe 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 \f(CI\*(C`caller\*(C'\fI package) in the argument hash, to see if an initializer
with that key has been defined. Finally, \f(CI\*(C`extract_initializers_for()\*(C'\fI
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.\fR
.RE
.RE
.RS 4
.Sp
In other words, given:
.Sp
.Vb 3
\&    my $arg_ref = {
\&        key_1 => \*(Aqgeneric value 1\*(Aq,
\&        key_2 => \*(Aqgeneric value 2\*(Aq,
\&
\&        \*(AqBase::Class\*(Aq => {
\&            key_1 => \*(Aqbase value 1\*(Aq
\&        },
\&
\&        \*(AqDer::Class\*(Aq => {
\&            key_1 => \*(Aqder value 1\*(Aq
\&            key_2 => \*(Aqder value 2\*(Aq
\&        },
\&    };
\&
\&    package Base::Class;
\&    use Class::Std::Utils;
\&
\&    my %base_args = extract_initializers_from($arg_ref);
\&
\&    package Der::Class;
\&    use Class::Std::Utils;
\&
\&    my %der_args = extract_initializers_from($arg_ref);
.Ve
.Sp
then \f(CW%base_args\fR would be initialized to:
.Sp
.Vb 3
\&    (
\&        key_1 => \*(Aqbase value 1\*(Aq,
\&        key_2 => \*(Aqgeneric value 2\*(Aq,
\&
\&        \*(AqBase::Class\*(Aq => {
\&            key_1 => \*(Aqbase value 1\*(Aq,
\&        },
\&
\&        \*(AqDer::Class\*(Aq => {
\&            key_1 => \*(Aqder value 1\*(Aq,
\&            key_2 => \*(Aqder value 2\*(Aq,
\&        },
\&    )
.Ve
.Sp
whilst \f(CW%der_args\fR would be initialized to:
.Sp
.Vb 3
\&    (
\&        key_1 => \*(Aqder value 1\*(Aq,
\&        key_2 => \*(Aqder value 2\*(Aq,
\&
\&        \*(AqBase::Class\*(Aq => {
\&            key_1 => \*(Aqbase value 1\*(Aq,
\&        },
\&
\&        \*(AqDer::Class\*(Aq => {
\&            key_1 => \*(Aqder value 1\*(Aq,
\&            key_2 => \*(Aqder value 2\*(Aq,
\&        },
\&    )
.Ve
.Sp
That is, the top-level entries would be replaced by any second-level
entries with the same key that appear in a top-level entry of the same name as
the calling package.
.Sp
This means that each class can just refer to \f(CW$args{key_1}\fR and
\&\f(CW$args{key_2}\fR and be confident that the resulting values will be the
most specific available for that class.
.RE
.SH "DIAGNOSTICS"
.IX Header "DIAGNOSTICS"
.ie n .IP """%s initializer must be a nested hash""" 4
.el .IP "\f(CW%s initializer must be a nested hash\fR" 4
.IX Item "%s initializer must be a nested hash"
Thrown by \f(CW\*(C`extract_initializers_from()\*(C'\fR. 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.
.SH "CONFIGURATION AND ENVIRONMENT"
.IX Header "CONFIGURATION AND ENVIRONMENT"
Class::Std::Utils requires no configuration files or environment variables.
.SH "DEPENDENCIES"
.IX Header "DEPENDENCIES"
Thsi module requires both the \f(CW\*(C`Scalar::Util\*(C'\fR and \f(CW\*(C`List::Util\*(C'\fR modules,
which are standard in Perl 5.8 and available from the \s-1CPAN\s0 for earlier
versions of Perl.
.SH "INCOMPATIBILITIES"
.IX Header "INCOMPATIBILITIES"
None reported.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
The \f(CW\*(C`Class::Std\*(C'\fR module
.PP
\&\*(L"Perl Best Practices\*(R", O'Reilly, 2005.
.SH "BUGS AND LIMITATIONS"
.IX Header "BUGS AND LIMITATIONS"
No bugs have been reported.
.PP
Please report any bugs or feature requests to
\&\f(CW\*(C`bug\-class\-std\-utils@rt.cpan.org\*(C'\fR, or through the web interface at
<http://rt.cpan.org>.
.SH "AUTHOR"
.IX Header "AUTHOR"
Damian Conway  \f(CW\*(C`<DCONWAY@cpan.org>\*(C'\fR
.SH "LICENCE AND COPYRIGHT"
.IX Header "LICENCE AND COPYRIGHT"
Copyright (c) 2005, Damian Conway \f(CW\*(C`<DCONWAY@cpan.org>\*(C'\fR. All rights reserved.
.PP
This module is free software; you can redistribute it and/or
modify it under the same terms as Perl itself.
.SH "DISCLAIMER OF WARRANTY"
.IX Header "DISCLAIMER OF WARRANTY"
\&\s-1BECAUSE 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 \*(L"AS IS\*(R" 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.\s0
.PP
\&\s-1IN 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\s0 (\s-1INCLUDING 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\s0), \s-1EVEN IF
SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF
SUCH DAMAGES.\s0