Perl Cd Bookshelf [Electronic resources]

32.6. Class::Struct

use Class::Struct;
struct Manager => { # Creates a Manager->new() constructor.
name    => ''$'',  # Now name() method accesses a scalar value.
salary  => ''$'',  # And so does salary().
started => ''$'', # And so does started().
};
struct Shoppe => {# Creates a Shoppe->new() constructor.
owner   => ''$'',# Now owner() method accesses a scalar.
addrs   => ''@'', # And addrs() method accesses an array.
stock   => ''%'',# And stock() method accesses a hash.
boss    => ''Manager'',  
 # Initializes with Manager->new().
};
$store = Shoppe->new();
$store->owner(''Abdul Alhazred'');
$store->addrs(0, ''Miskatonic University'');
$store->addrs(1, ''Innsmouth, Mass.'');
$store->stock("books", 208);
$store->stock("charms", 3);
$store->stock("potions", "none");
$store->boss->name(''Prof L. P. Haitch'');
$store->boss->salary(''madness'');
$store->boss->started(scalar localtime);

The Class::Struct module provides a way to "declare" a class as having objects whose fields are of a specific type. The function that does this is called struct. Because structures or records are not base types in Perl, each time you want to create a class to provide a record-like data object, you have to define a constructor method along with accessor methods for each data field, sometimes called "wrapper" methods. The Class::Struct module''s struct function alleviates this tedium by creating a class for you on the fly. You just tell it what data members should exist and their types. The function creates a constructor method named new in the package specified by the first argument, plus an attribute accessor method for each member, as specified by the second argument, which should be a hash reference.

Field types are specified as either a built-in type using the customary "$", "@", "%", and "&" symbols, or as another class using the class name. The type of each field will be enforced when you try to set the value.

Many standard modules use Class::Struct to create their objects and accessors, including Net::hostent and User::pwent, whose source you can look at as a model. See also the CPAN modules Tie::SecureHash and Class::Multimethods for more elaborate approaches to autogeneration of classes and accessor methods. See the section "Managing Instance Data" in Chapter 12, "Objects".