Provided by: libclass-meta-perl_0.66-3_all bug

NAME

       Class::Meta::AccessorBuilder::Affordance - Affordance style accessor generation

SYNOPSIS

         package MyApp::TypeDef;

         use strict;
         use Class::Meta::Type;
         use IO::Socket;

         my $type = Class::Meta::Type->add(
             key     => 'io_socket',
             builder => 'affordance',
             desc    => 'IO::Socket object',
             name    => 'IO::Socket Object'
         );

DESCRIPTION

       This module provides the an affordance style accessor builder for Class::Meta.  Affordance
       accessors are attribute accessor methods that separate the getting and setting of an
       attribute value into distinct methods. The approach both eliminates the overhead of
       checking to see whether an accessor is called as a getter or a setter, which is common for
       Perl style accessors, while also creating a psychological barrier to accidentally misusing
       an attribute.

   Accessors
       Class::Meta::AccessorBuilder::Affordance create two different types of accessors: getters
       and setters. The type of accessors created depends on the value of the "authz" attribute
       of the Class::Meta::Attribute for which the accessor is being created.

       For example, if the "authz" is Class::Meta::RDWR, then two accessor methods will be
       created:

         my $value = $obj->get_io_socket;
         $obj->set_io_socket($value);

       If the value of "authz" is Class::Meta::READ, then only the get method will be created:

         my $value = $obj->io_socket;

       And finally, if the value of "authz" is Class::Meta::WRITE, then only the set method will
       be created (why anyone would want this is beyond me, but I provide for the sake of
       completeness):

         my $value = $obj->io_socket;

   Data Type Validation
       Class::Meta::AccessorBuilder::Affordance uses all of the validation checks passed to it to
       validate new values before assigning them to an attribute. It also checks to see if the
       attribute is required, and if so, adds a check to ensure that its value is never
       undefined. It does not currently check to ensure that private and protected methods are
       used only in their appropriate contexts, but may do so in a future release.

   Class Attributes
       If the "context" attribute of the attribute object for which accessors are to be built is
       "Class::Meta::CLASS", Class::Meta::AccessorBuilder will build accessors for a class
       attribute instead of an object attribute. Of course, this means that if you change the
       value of the class attribute in any context--whether via a an object, the class name, or
       an an inherited class name or object, the value will be changed everywhere.

       For example, for a class attribute "count", you can expect the following to work:

         MyApp::Custom->set_count(10);
         my $count = MyApp::Custom->get_count; # Returns 10.
         my $obj = MyApp::Custom->new;
         $count = $obj->get_count;             # Returns 10.

         $obj->set_count(22);
         $count = $obj->get_count;             # Returns 22.
         my $count = MyApp::Custom->get_count; # Returns 22.

         MyApp::Custom->set_count(35);
         $count = $obj->get_count;             # Returns 35.
         my $count = MyApp::Custom->get_count; # Returns 35.

       Currently, class attribute accessors are not designed to be inheritable in the way
       designed by Class::Data::Inheritable, although this might be changed in a future release.
       For now, I expect that the current simple approach will cover the vast majority of
       circumstances.

       Note: Class attribute accessors will not work accurately in multiprocess environments such
       as mod_perl. If you change a class attribute's value in one process, it will not be
       changed in any of the others. Furthermore, class attributes are not currently shared
       across threads. So if you're using Class::Meta class attributes in a multi-threaded
       environment (such as iThreads in Perl 5.8.0 and later) the changes to a class attribute in
       one thread will not be reflected in other threads.

Private and Protected Attributes

       Any attributes that have their "view" attribute set to Class::Meta::Private or
       Class::Meta::Protected get additional validation installed to ensure that they're truly
       private and protected. This includes when they are set via parameters to constructors
       generated by Class::Meta. The validation is performed by checking the caller of the
       accessors, and throwing an exception when the caller isn't the class that owns the
       attribute (for private attributes) or when it doesn't inherit from the class that owns the
       attribute (for protected attributes).

       As an implementation note, this validation is performed for parameters passed to
       constructors created by Class::Meta by ignoring looking for the first caller that isn't
       Class::Meta::Constructor:

         my $caller = caller;
         # Circumvent generated constructors.
         for (my $i = 1; $caller eq 'Class::Meta::Constructor'; $i++) {
             $caller = caller($i);
         }

       This works because Class::Meta::Constructor installs the closures that become
       constructors, and thus, when those closures call accessors to set new values for
       attributes, the caller is Class::Meta::Constructor. By going up the stack until we find
       another package, we correctly check to see what context is setting attribute values via a
       constructor, rather than the constructor method itself being the context.

       This is a bit of a hack, but since Perl uses call stacks for checking security in this
       way, it's the best I could come up with. Other suggestions welcome. Or see
       Class::Meta::Type to create your own accessor generation code

INTERFACE

       The following functions must be implemented by any Class::Meta accessor generation module.

   Functions
       build_attr_get

         my $code = Class::Meta::AccessorBuilder::Affordance::build_attr_get();

       This function is called by "Class::Meta::Type::make_attr_get()" and returns a code
       reference that can be used by the "get()" method of Class::Meta::Attribute to return the
       value stored for that attribute for the object passed to the code reference.

       build_attr_set

         my $code = Class::Meta::AccessorBuilder::Affordance::build_attr_set();

       This function is called by "Class::Meta::Type::make_attr_set()" and returns a code
       reference that can be used by the "set()" method of Class::Meta::Attribute to set the
       value stored for that attribute for the object passed to the code reference.

       build

         Class::Meta::AccessorBuilder::Affordance::build(
             $pkg, $attribute, $create, @checks
         );

       This method is called by the "build()" method of Class::Meta::Type, and does the work of
       actually generating the accessors for an attribute object. The arguments passed to it are:

       $pkg
           The name of the class to which the accessors will be added.

       $attribute
           The Class::Meta::Attribute object that specifies the attribute for which the accessors
           will be created.

       $create
           The value of the "create" attribute of the Class::Meta::Attribute object, which
           determines what accessors, if any, are to be created.

       @checks
           A list of code references that validate the value of an attribute. These will be used
           in the set accessor (mutator) to validate new attribute values.

SUPPORT

       This module is stored in an open GitHub repository <http://github.com/theory/class-meta/>.
       Feel free to fork and contribute!

       Please file bug reports via GitHub Issues <http://github.com/theory/class-meta/issues/> or
       by sending mail to bug-Class-Meta@rt.cpan.org <mailto:bug-Class-Meta@rt.cpan.org>.

AUTHOR

       David E. Wheeler <david@justatheory.com>

SEE ALSO

       Class::Meta
           This class contains most of the documentation you need to get started with
           Class::Meta.

       Class::Meta::AccessorBuilder
           This module generates Perl style accessors.

       Class::Meta::Type
           This class manages the creation of data types.

       Class::Meta::Attribute
           This class manages Class::Meta class attributes, most of which will have generated
           accessors.

COPYRIGHT AND LICENSE

       Copyright (c) 2002-2011, David E. Wheeler. Some Rights Reserved.

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

perl v5.34.0                                2022-06-Class::Meta::AccessorBuilder::Affordance(3pm)