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.\" ========================================================================
.\"
.IX Title "Class::Std::Utils 3pm"
.TH Class::Std::Utils 3pm "2008-09-09" "perl v5.10.0" "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\s0 \s-1THIS\s0 \s-1SOFTWARE\s0 \s-1IS\s0 \s-1LICENSED\s0 \s-1FREE\s0 \s-1OF\s0 \s-1CHARGE\s0, \s-1THERE\s0 \s-1IS\s0 \s-1NO\s0 \s-1WARRANTY\s0
\&\s-1FOR\s0 \s-1THE\s0 \s-1SOFTWARE\s0, \s-1TO\s0 \s-1THE\s0 \s-1EXTENT\s0 \s-1PERMITTED\s0 \s-1BY\s0 \s-1APPLICABLE\s0 \s-1LAW\s0. \s-1EXCEPT\s0 \s-1WHEN\s0
\&\s-1OTHERWISE\s0 \s-1STATED\s0 \s-1IN\s0 \s-1WRITING\s0 \s-1THE\s0 \s-1COPYRIGHT\s0 \s-1HOLDERS\s0 \s-1AND/OR\s0 \s-1OTHER\s0 \s-1PARTIES\s0
\&\s-1PROVIDE\s0 \s-1THE\s0 \s-1SOFTWARE\s0 \*(L"\s-1AS\s0 \s-1IS\s0\*(R" \s-1WITHOUT\s0 \s-1WARRANTY\s0 \s-1OF\s0 \s-1ANY\s0 \s-1KIND\s0, \s-1EITHER\s0
\&\s-1EXPRESSED\s0 \s-1OR\s0 \s-1IMPLIED\s0, \s-1INCLUDING\s0, \s-1BUT\s0 \s-1NOT\s0 \s-1LIMITED\s0 \s-1TO\s0, \s-1THE\s0 \s-1IMPLIED\s0
\&\s-1WARRANTIES\s0 \s-1OF\s0 \s-1MERCHANTABILITY\s0 \s-1AND\s0 \s-1FITNESS\s0 \s-1FOR\s0 A \s-1PARTICULAR\s0 \s-1PURPOSE\s0. \s-1THE\s0
\&\s-1ENTIRE\s0 \s-1RISK\s0 \s-1AS\s0 \s-1TO\s0 \s-1THE\s0 \s-1QUALITY\s0 \s-1AND\s0 \s-1PERFORMANCE\s0 \s-1OF\s0 \s-1THE\s0 \s-1SOFTWARE\s0 \s-1IS\s0 \s-1WITH\s0
\&\s-1YOU\s0. \s-1SHOULD\s0 \s-1THE\s0 \s-1SOFTWARE\s0 \s-1PROVE\s0 \s-1DEFECTIVE\s0, \s-1YOU\s0 \s-1ASSUME\s0 \s-1THE\s0 \s-1COST\s0 \s-1OF\s0 \s-1ALL\s0
\&\s-1NECESSARY\s0 \s-1SERVICING\s0, \s-1REPAIR\s0, \s-1OR\s0 \s-1CORRECTION\s0.
.PP
\&\s-1IN\s0 \s-1NO\s0 \s-1EVENT\s0 \s-1UNLESS\s0 \s-1REQUIRED\s0 \s-1BY\s0 \s-1APPLICABLE\s0 \s-1LAW\s0 \s-1OR\s0 \s-1AGREED\s0 \s-1TO\s0 \s-1IN\s0 \s-1WRITING\s0
\&\s-1WILL\s0 \s-1ANY\s0 \s-1COPYRIGHT\s0 \s-1HOLDER\s0, \s-1OR\s0 \s-1ANY\s0 \s-1OTHER\s0 \s-1PARTY\s0 \s-1WHO\s0 \s-1MAY\s0 \s-1MODIFY\s0 \s-1AND/OR\s0
\&\s-1REDISTRIBUTE\s0 \s-1THE\s0 \s-1SOFTWARE\s0 \s-1AS\s0 \s-1PERMITTED\s0 \s-1BY\s0 \s-1THE\s0 \s-1ABOVE\s0 \s-1LICENCE\s0, \s-1BE\s0
\&\s-1LIABLE\s0 \s-1TO\s0 \s-1YOU\s0 \s-1FOR\s0 \s-1DAMAGES\s0, \s-1INCLUDING\s0 \s-1ANY\s0 \s-1GENERAL\s0, \s-1SPECIAL\s0, \s-1INCIDENTAL\s0,
\&\s-1OR\s0 \s-1CONSEQUENTIAL\s0 \s-1DAMAGES\s0 \s-1ARISING\s0 \s-1OUT\s0 \s-1OF\s0 \s-1THE\s0 \s-1USE\s0 \s-1OR\s0 \s-1INABILITY\s0 \s-1TO\s0 \s-1USE\s0
\&\s-1THE\s0 \s-1SOFTWARE\s0 (\s-1INCLUDING\s0 \s-1BUT\s0 \s-1NOT\s0 \s-1LIMITED\s0 \s-1TO\s0 \s-1LOSS\s0 \s-1OF\s0 \s-1DATA\s0 \s-1OR\s0 \s-1DATA\s0 \s-1BEING\s0
\&\s-1RENDERED\s0 \s-1INACCURATE\s0 \s-1OR\s0 \s-1LOSSES\s0 \s-1SUSTAINED\s0 \s-1BY\s0 \s-1YOU\s0 \s-1OR\s0 \s-1THIRD\s0 \s-1PARTIES\s0 \s-1OR\s0 A
\&\s-1FAILURE\s0 \s-1OF\s0 \s-1THE\s0 \s-1SOFTWARE\s0 \s-1TO\s0 \s-1OPERATE\s0 \s-1WITH\s0 \s-1ANY\s0 \s-1OTHER\s0 \s-1SOFTWARE\s0), \s-1EVEN\s0 \s-1IF\s0
\&\s-1SUCH\s0 \s-1HOLDER\s0 \s-1OR\s0 \s-1OTHER\s0 \s-1PARTY\s0 \s-1HAS\s0 \s-1BEEN\s0 \s-1ADVISED\s0 \s-1OF\s0 \s-1THE\s0 \s-1POSSIBILITY\s0 \s-1OF\s0
\&\s-1SUCH\s0 \s-1DAMAGES\s0.