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.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'); $store->boss->started(scalar localtime);
Field types are specified as either a built-in type using the customary "$", "@", "%", 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".
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