1) get and set methods for simple attributes can be automatically generated 2) argument lists are handled as described below 3) the protocol for object creation and initialization is close to the 'textbook' approach generally suggested for object-oriented Perl (see below) 4) object initialization is handled correctly in the presence of multiple inheritance @AUTO_ATTRIBUTES is a list of 'attribute' names: get and set methods are created for each attribute. By default, the name of the method is identical to the attribute (but see $CASE below). Values of attributes can be set via the 'new' constructor, %DEFAULTS, or the 'set' method as discussed below. @CLASS_ATTRIBUTES is a list of class attributes: get and set methods are created for each attribute. By default, the name of the method is identical to the attribute (but see $CASE below). Values of attributes can be set via the 'new' constructor, %DEFAULTS (initialized at "declare time" (when the declare function is called) versus instance attributes, which are of course initialized at runtime), standard class variable access syntax ($PackageName::AttributeName), or the 'set' method as discussed below. Normal inheritance rules apply to class attributes (but of course, instances of the same class share the same class variable). @OTHER_ATTRIBUTES is a list of attributes for which get and set methods are NOT generated, but whose values can be set via the 'new' constructor or the 'set' method as discussed below. %SYNONYMS is a hash that defines synonyms for attribues. Each entry is of the form 'new_attribute_name'=>'old_attribute_name'. get and set methods are generated for the new names; these methods simply call the method for the old name. %DEFAULTS is a hash that defines default values for attributes. Each entry is of the form 'attribute_name'=>'default_value'. get and set methods are generated for each attributes. $CASE controls whether additional methods are generated with all upper or all lower case names. It should be a string containing the strings 'upper' or 'lower' (case insenstive) if the desired case is desired. The declare function actually generates the method. This should be called once and no where else. AutoClass must be the first class in @ISA !! As usual, you create objects by calling 'new'. Since AutoClass is the first class in @ISA, it's 'new' method is the one that's called. AutoClass's 'new' examines the rest of @ISA and searches for a superclass that is capable of creating the object. If no such superclass is found, AutoClass creates the object itself. Once the object is created, AutoClass arranges to have all subclasses run their initialization methods (_init_self) in a top-down order.
We support positional and keyword argument lists, but we strongly urge that each method pick one form or the other, as the combination is inherently ambiguous (see below).
Consider a method, foo, that takes two arguments, a first name and a last_name name. The positional form might be
$object->foo('Nat', 'Goodman')
while the keyword form might be
$object->foo(first_name=>'Nat', last_name=>'Goodman')
In keyword form, keywords are insensitive to case and leading dashes: the keywords
first_name, -first_name, -FIRST_NAME, --FIRST_NAME, First_Name, -First_Name
are all equivalent. Internally, for those who care, our convention is to use uppercase, un-dashed keys for the attributes of an object.
We convert repeated keyword arguments into an ARRAY ref of the values. Thus:
$object->foo(first_name=>'Nat', first_name=>'Nathan')
is equivalent to
$object->foo(first_name=>['Nat', 'Nathan'])
Keyword arguments can be specified via ARRAY or HASH refs which are dereferenced back to their elements, e.g.,
$object->foo([first_name=>'Nat', last_name=>'Goodman']) $object->foo({first_name=>'Nat', last_name=>'Goodman'})
are both equivalent to
We can get away with this, because we encourage method writers to choose between positional and keyword argument lists. If a method uses positional arguments, it will interpret
$object->foo($array)
as a call that is setting the first_name parameter to $array, while if it uses keyword arguments, it will dereference the array to a list of keyword, value pairs.
We also allow the argument list to be an object. This is often used in new to accomplish what a C++ programmer would call a cast. In simple cases, the object is just treated as a HASH ref and its attributes are passed to a the method as keyword, value pairs.
The keyword => value notation is just a Perl shorthand for stating two list members with the first one quoted. Thus,
is completely equivalent to
$object->foo('first_name', 'Nat', 'last_name', 'Goodman')
The ambiguity of allowing both positional and keyword forms should now be apparent. In this example,
$object->foo('first_name', 'Nat')
there is s no way to tell whether the program is calling foo with the first_name parameter set to the value 'first_name' and the last_name parameter set to 'Nat', vs. calling foo with the first_name parameter set to 'Nat' and the last_name parameter left undefined.
If a program wishes to permit both forms, we suggest that keywords be required to start with '-' (and that values do not start with '-'). Obviously, this is not fully general. We provide a method, _is_positional, that checks this convention. Subclasses are free to ignore this.
We expect objects to be created by invoking new on its class. For example
$object = new SomeClass(first=>'Nat', last=>'Goodman')
To correctly initialize objects that participate in multiple inheritance, we use a technqiue described in Chapter 10 of Paul Fenwick's excellent tutorial on Object Oriented Perl (see http://perltraining.com.au/notes/perloo.pdf). (We experimented with Damian Conway's interesting NEXT pseudo-pseudo-class discussed in Chapter 11 of Fenwick's tutorial available in CPAN at http://search.cpan.org/author/DCONWAY/NEXT-0.50/lib/NEXT.pm, but could not get it to traverse the inheritance structure in the correct, top-down order.)
AutoClass class provides a 'new' method that expects a keyword argument list. This method processes the argument list as discussed in L<Argument Processing>: it figures out the syntactic form (list of keyword, value pairs, vs. ARRAY ref vs. HASH ref, etc.). It then converts the argument list into a canonical form, which is a list of keyword, value pairs with all keywords uppercased and de-dashed. Once the argument list is in this form, subsequent code treats it as a HASH ref.
AutoClass::new initializes the object's class structure from top to bottom, and is careful to initialize each class exactly once even in the presence of multiple inheritance. The net effect is that objects are initialized top-down as expected; a subclass object can assume that all superior classes are initialized by the time subclass initialization occurs.
AutoClass automatically initializes attributes and synonyms declared when the class is defined. If additional initialization is required, the class writer can provide an _init_self method. _init_self is called after all superclasses are initialized and after the automatic initialization for the class has been done.
AutoClass initializes attributes and synonyms by calling the set methods for these elements with the like-named parameter -- it does not simply slam the parameter into a slot in the object''s HASH. This allows the class writer implement non-standard initialization within the set method.
The main case where a subclass needs its own 'new' method is if it wishes to allow positional arguments. In this case, the subclass 'new' is responsible for is responsible for recognizing that positional arguments are being used (if the class permits keyword arguments also), and converting the positional arguments into keyword, value form. At this point, the method can simply call AutoClass::new with the converted argument list.
The subclass should not generally call SUPER::new as this would force redundant argument processing in any super-class that also has its own new. It would also force the super-class new to be smart enough to handle positional as well as keyword parameters, which as we've noted is inherently ambiguous.
=head1 KNOWN BUGS AND CAVEATS This is still a work in progress. =head2 Bugs, Caveats, and ToDos 1) There is no way to manipulate the arguments that are sent to the real base class. There should be a way to specify a subroutine that reformats these if needed. 2) DESTROY not handled 3) Autogeneration of methods is hand crafted. It may be better to use Class::MakeMethods or Damian Conway's Multimethod class for doing signature-based method dispatch 4) Caveat: In order to specify that a class that uses AutoClass should return undef (versus an uninitialized (but blessed) object), one need to set: $self->{__NULLIFY__}=1;
Email natg@shore.net
Email ccavnor@systemsbiology.net
Copyright (c) 2003 Institute for Systems Biology (ISB). All Rights Reserved.
This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
The rest of the documentation describes the methods. Note that internal methods are preceded with _
Title : new Usage : $object=new Foo(first_name=>'Nat', last_name=>'Goodman') where Foo is a subclass of AutoClass Function: Create and initialize object Returns : New object of class $class Args : Any arguments needed by subclasses -->> Arguments must be in keyword form. See DESCRIPTION for more. Notes : Tries to invoke superclass to actually create the object
Title : _init Usage : $self->_init($class,$args) Function: Initialize new object Returns : nothing useful Args : $class -- lexical (static) class being initialized, not the actual (dynamic) class of $self $arg -- argument list in canonical keyword form Notes : Adapted from Chapter 10 of Paul Fenwick''s excellent tutorial on Object Oriented Perl (see http://perltraining.com.au/notes/perloo.pdf).
Title : set Usage : $self->set(-first_name=>'Nat',-last_name=>'Goodman') Function: Set multiple attributes in existing object Args : Parameter list in same format as for new Returns : nothing
Title : set_attributes Usage : $self->set_attributes([qw(first_name last_name)],$args) Function: Set multiple attributes from a Class::AutoClass::Args object Any attribute value that is present in $args is set Args : ARRAY ref of attributes Class::AutoClass::Args object Returns : nothing
Title : get Usage : ($first,$last)=$self->get(qw(-first_name,-last_name)) Function: Get values for multiple attributes Args : Attribute names Returns : List of attribute values
Title : AUTO_ATTRIBUTES Usage : @auto_attributes=AUTO_ATTRIBUTES('SubClass') @auto_attributes=$self->AUTO_ATTRIBUTES(); Function: Get @AUTO_ATTRIBUTES for lexical class. @AUTO_ATTRIBUTES is defined by class writer. These are attributes for which get and set methods are automatically generated. _init automatically initializes these attributes from like-named parameters in the argument list Args : class
Title : OTHER_ATTRIBUTES Usage : @other_attributes=OTHER_ATTRIBUTES('SubClass') @other_attributes=$self->OTHER_ATTRIBUTES(); Function: Get @OTHER_ATTRIBUTES for lexical class. @OTHER_ATTRIBUTES is defined by class writer. These are attributes for which get and set methods are not automatically generated. _init automatically initializes these attributes from like-named parameters in the argument list Args : class
Title : SYNONYMS Usage : %synonyms=SYNONYMS('SubClass') %synonyms=$self->SYNONYMS(); Function: Get %SYNONYMS for lexical class. %SYNONYMS is defined by class writer. These are alternate names for attributes generally defined in superclasses. get and set methods are automatically generated. _init automatically initializes these attributes from like-named parameters in the argument list Args : class
Title : declare Usage : @AUTO_ATTRIBUTES=qw(sex address dob); @OTHER_ATTRIBUTES=qw(age); %SYNONYMS=(name=>'id'); AutoClass::declare(__PACKAGE__,'lower|upper'); Function: Generate get and set methods for simple attributes and synonyms. Method names are identical to the attribute names including case Returns : nothing Args : lexical class being created -- should always be __PACKAGE__ ARRAY ref of attributes HASH ref of synonyms. Keys are new names, values are old code that indicates whether method should also be generated with all lower or upper case names
Title : _enumerate Usage : _enumerate($class); Function: locates classes that have a callable constructor Args : a class reference Returns : list of internal classes, a class with a callable constructor
Title : _fix_args Usage : $args=_fix_args(-name=>'Nat',-name=>Goodman,address=>'Seattle') $args=$self->_fix_args(@args) Function: Convert argument list into canonical form. This is a HASH ref in which keys are uppercase with no leading dash, and repeated keyword arguments are merged into an ARRAY ref. In the example above, the argument list would be converted to this hash (NAME=>['Nat', 'Goodman'],ADDRESS=>'Seattle') Returns : argument list in canonical form Args : argument list in any keyword form
Title : _fix_keyword Usage : $keyword=_fix_keyword('-name') @keywords=_fix_keyword('-name','-address'); Function: Convert a keyword or list of keywords into canonical form. This is uppercase with no leading dash. In the example above, '-name' would be converted to 'NAME'. Non-scalars are left unchanged. Returns : keyword or list of keywords in canonical form Args : keyword or list of keywords
Title : _set_attributes Usage : my %synonyms=SYNONYMS($class); my $attributes=[AUTO_ATTRIBUTES($class), OTHER_ATTRIBUTES($class), keys %synonyms]; $self->_set_attributes($attributes,$args); Function: Set a list of simple attributes from a canonical argument list Returns : nothing Args : $attributes -- ARRAY ref of attributes to be set $args -- argument list in canonical keyword (hash) form Notes : The function calls the set method for each attribute passing it the like-named parameter from the argument list
Title : _is_positional Usage : if (_is_positional(@args)) { ($arg1,$arg2,$arg3)=@args; } Function: Checks whether an argument list conforms to our convention for positional arguments. The function returns true if (1) the argument list has an odd number of elements, or (2) the first argument starts with a dash ('-'). Obviously, this is not fully general. Returns : boolean Args : argument list Notes : As explained in DESCRIPTION, we recommend that methods not support both positional and keyford argument lists, as this is inherently ambiguous. BUGS : NOT YET TESTED in this version
Title : set_class_defaults Usage : $self->set_class_defaults($attributes,$class,$args); Function: Set default values for class argument Args : reference to the class and a Class::AutoClass::Args object which contains the arguments to set Returns : nothing
To install Class::AutoClass, copy and paste the appropriate command in to your terminal.
cpanm
cpanm Class::AutoClass
CPAN shell
perl -MCPAN -e shell install Class::AutoClass
For more information on module installation, please visit the detailed CPAN module installation guide.