Class::Std::Utils
Class::Std::Utils(3) User Contributed Perl Documentation Class::Std::Utils(3)
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 cre-
ation 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 ref-
erence-- and acts exactly like the "Scalar::Util::refaddr()",
returning a unique integer value suitable for identifying the ref-
erent.
"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 vari-
ables.
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.
SEE ALSO
The "Class::Std" module
"Perl Best Practices", O’Reilly, 2005.
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
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.
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 REN-
DERED 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.
perl v5.8.8 2007-11-24 Class::Std::Utils(3)
