Class::Struct (Perl in a Nutshell, 2nd Edition)

struct

struct (paramlist)

Creates a class, with object methods for each element of the class. The parameter list paramlist can take one of three forms:

struct( CLASS_NAME => [ ELEMENT_LIST ]); 
# Object is array-based
struct( CLASS_NAME => { ELEMENT_LIST }); 
# Object is hash-based
struct( ELEMENT_LIST );     # Class name is current, and package name          
      # object is array-based

The array-based element lists are faster and smaller, but the hash-based list is more flexible. The class that is created can be a subclass of the UNIVERSAL class, but not of any other class.

Element list

The items in the ELEMENT_LIST are of the form:

NAME => TYPE, ...

in which each NAME=>TYPE pair declares one element of the struct. Each element name is defined as an accessor method, unless a method is explicitly defined with that name. (In that case, a warning is issued if the -w flag is set.)

Element types and accessor methods

There are four possible element types, each represented by a string. Each string may start with an asterisk (*), indicating that a reference to the element will be returned. The type of an element determines the accessor method provided. The following list shows the element types, the strings that represent them, and the accessor:

array (@ or *@): The element is an array, initialized to ( ). With no argument, the accessor returns a reference to the element's whole array. With one or two arguments, the first argument is an index specifying one element of the array; the second argument, if present, is the value that will be assigned to that array element.
class (Class_Name or *Class_Name): The element's value must be a reference blessed to the named class or to one of its subclasses. The element is initialized to the result of calling the new constructor of the named class. The accessor's argument, if any, is the value that will be assigned to the element. The accessor croak s if it's not an appropriate object reference.
hash (% or *%): The element is a hash, initialized to ( ). With no argument, the accessor returns a reference to the element's whole hash. With one or two arguments, the first argument is a key specifying one element of the hash; the second argument, if present, is the value to be assigned to that hash element.
scalar ($ or *$): The element is a scalar, initialized to undef. The accessor's argument, if any, is assigned to the element.

8.43. Class::Struct

Element list

Element types and accessor methods