MAN page from RedHat Other perl-5.004-0.1.i386.rpm

Class::Struct

Section: Perl Programmers Reference Guide (3)
Updated: perl 5.004, patch 04
Index

NAME

Class::Struct - declare struct-like datatypes as Perl classes

SYNOPSIS

    use Class::Struct;            # declare struct, based on array:    struct( CLASS_NAME => [ ELEMENT_NAME => ELEMENT_TYPE, ... ]);            # declare struct, based on hash:    struct( CLASS_NAME => { ELEMENT_NAME => ELEMENT_TYPE, ... });

    package CLASS_NAME;    use Class::Struct;            # declare struct, based on array, implicit class name:    struct( ELEMENT_NAME => ELEMENT_TYPE, ... );

    package Myobj;    use Class::Struct;            # declare struct with four types of elements:    struct( s => '$', a => '@', h => '%', c => 'My_Other_Class' );

    $obj = new Myobj;               # constructor

                                    # scalar type accessor:    $element_value = $obj->s;           # element value    $obj->s('new value');               # assign to element

                                    # array type accessor:    $ary_ref = $obj->a;                 # reference to whole array    $ary_element_value = $obj->a(2);    # array element value    $obj->a(2, 'new value');            # assign to array element

                                    # hash type accessor:    $hash_ref = $obj->h;                # reference to whole hash    $hash_element_value = $obj->h('x'); # hash element value    $obj->h('x', 'new value');        # assign to hash element

                                    # class type accessor:    $element_value = $obj->c;           # object reference    $obj->c->method(...);               # call method of object    $obj->c(new My_Other_Class);        # assign a new object

DESCRIPTION

Class::Struct exports a single function, struct.Given a list of element names and types, and optionallya class name, struct creates a Perl 5 class that implementsa ``struct-like'' data structure.

The new class is given a constructor method, new, for creatingstruct objects.

Each element in the struct data has an accessor method, which isused to assign to the element and to fetch its value. Thedefault accessor can be overridden by declaring a sub of thesame name in the package. (See Example 2.)

Each element's type can be scalar, array, hash, or class.

The struct() function

The struct function has three forms of parameter-list.

    struct( CLASS_NAME => [ ELEMENT_LIST ]);    struct( CLASS_NAME => { ELEMENT_LIST });    struct( ELEMENT_LIST );

The first and second forms explicitly identify the name of theclass being created. The third form assumes the current packagename as the class name.

An object of a class created by the first and third forms isbased on an array, whereas an object of a class created by thesecond form is based on a hash. The array-based forms will besomewhat faster and smaller; the hash-based forms are moreflexible.

The class created by struct must not be a subclass of anotherclass other than UNIVERSAL.

A function named new must not be explicitly defined in a classcreated by struct.

The ELEMENT_LIST has the form

    NAME => TYPE, ...

Each name-type pair declares one element of the struct. Eachelement name will be defined as an accessor method unless amethod by that name is explicitly defined; in the latter case, awarning is issued if the warning flag (-w) is set.

Element Types and Accessor Methods

The four element types -- scalar, array, hash, and class -- arerepresented by strings -- '$', '@', '%', and a class name --optionally preceded by a '*'.

The accessor method provided by struct for an element dependson the declared type of the element.

Scalar ('$' or '*$')

The element is a scalar, and is initialized to undef.

The accessor's argument, if any, is assigned to the element.

If the element type is '$', the value of the element (afterassignment) is returned. If the element type is '*$', a referenceto the element is returned.

Array ('@' or '*@')

The element is an array, initialized to ().

With no argument, the accessor returns a reference to theelement's whole array.

With one or two arguments, the first argument is an indexspecifying one element of the array; the second argument, ifpresent, is assigned to the array element. If the element typeis '@', the accessor returns the array element value. If theelement type is '*@', a reference to the array element isreturned.

Hash ('%' or '*%')

The element is a hash, initialized to ().

With no argument, the accessor returns a reference to theelement's whole hash.

With one or two arguments, the first argument is a key specifyingone element of the hash; the second argument, if present, isassigned to the hash element. If the element type is '%', theaccessor returns the hash element value. If the element type is'*%', a reference to the hash element is returned.

Class ('Class_Name' or '*Class_Name')

The element's value must be a reference blessed to the namedclass or to one of its subclasses. The element is initialized tothe result of calling the new constructor of the named class.

The accessor's argument, if any, is assigned to the element. Theaccessor will croak if this is not an appropriate objectreference.

If the element type does not start with a '*', the accessorreturns the element value (after assignment). If the element typestarts with a '*', a reference to the element itself is returned.

EXAMPLES

Example 1

Giving a struct element a class type that is also a struct is howstructs are nested. Here, timeval represents a time (seconds andmicroseconds), and rusage has two elements, each of which is oftype timeval.

    use Class::Struct;

    struct( rusage => {        ru_utime => timeval,  # seconds        ru_stime => timeval,  # microseconds    });

    struct( timeval => [        tv_secs  => '$',        tv_usecs => '$',    ]);

        # create an object:    my $t = new rusage;        # $t->ru_utime and $t->ru_stime are objects of type timeval.

        # set $t->ru_utime to 100.0 sec and $t->ru_stime to 5.0 sec.    $t->ru_utime->tv_secs(100);    $t->ru_utime->tv_usecs(0);    $t->ru_stime->tv_secs(5);    $t->ru_stime->tv_usecs(0);

Example 2

An accessor function can be redefined in order to provideadditional checking of values, etc. Here, we want the countelement always to be nonnegative, so we redefine the countaccessor accordingly.

    package MyObj;    use Class::Struct;

                # declare the struct    struct ( 'MyObj', { count => '$', stuff => '%' } );

                # override the default accessor method for 'count'    sub count {        my $self = shift;        if ( @_ ) {            die 'count must be nonnegative' if $_[0] < 0;            $self->{'count'} = shift;            warn "Too many args to count" if @_;        }        return $self->{'count'};    }

    package main;    $x = new MyObj;    print "\$x->count(5) = ", $x->count(5), "\n";                            # prints '$x->count(5) = 5'

    print "\$x->count = ", $x->count, "\n";                            # prints '$x->count = 5'

    print "\$x->count(-5) = ", $x->count(-5), "\n";                            # dies due to negative argument!

Author and Modification History

Renamed to Class::Struct and modified by Jim Miner, 1997-04-02.

    members() function removed.    Documentation corrected and extended.    Use of struct() in a subclass prohibited.    User definition of accessor allowed.    Treatment of '*' in element types corrected.    Treatment of classes as element types corrected.    Class name to struct() made optional.    Diagnostic checks added.

Originally Class::Template by Dean Roehrich.

    # Template.pm   --- struct/member template builder    #   12mar95    #   Dean Roehrich    #    # changes/bugs fixed since 28nov94 version:    #  - podified    # changes/bugs fixed since 21nov94 version:    #  - Fixed examples.    # changes/bugs fixed since 02sep94 version:    #  - Moved to Class::Template.    # changes/bugs fixed since 20feb94 version:    #  - Updated to be a more proper module.    #  - Added "use strict".    #  - Bug in build_methods, was using @var when @$var needed.    #  - Now using my() rather than local().    #    # Uses perl5 classes to create nested data types.    # This is offered as one implementation of Tom Christiansen's "structs.pl"    # idea.

This document was created byman2html,using the manual pages.