Class::Struct

Class::Struct(3)       Perl Programmers Reference Guide       Class::Struct(3)



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 optionally a class name, struct creates a
       Perl 5 class that implements a "struct-like" data structure.

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

       Each element in the struct data has an accessor method, which is used
       to assign to the element and to fetch its value.  The default accessor
       can be overridden by declaring a sub of the same 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 the class
       being created.  The third form assumes the current package name as the
       class name.

       An object of a class created by the first and third forms is based on
       an array, whereas an object of a class created by the second form is
       based on a hash. The array-based forms will be somewhat faster and
       smaller; the hash-based forms are more flexible.

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

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

       The ELEMENT_LIST has the form

           NAME => TYPE, ...

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

       Element Types and Accessor Methods

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

       The accessor method provided by struct for an element depends on 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 '$', the value of the element (after
            assignment) is returned. If the element type is '*$', a reference
            to the element is returned.

       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 assigned to the array element.  If the element type is
            '@', the accessor returns the array element value.  If the element
            type is '*@', a reference to the array element is returned.

       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
            assigned to the hash element.  If the element type is '%', the
            accessor 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 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 assigned to the element. The
            accessor will croak if this is not an appropriate object
            reference.

            If the element type does not start with a '*', the accessor
            returns the element value (after assignment). If the element type
            starts 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 how
            structs are nested.  Here, timeval represents a time (seconds and
            microseconds), and rusage has two elements, each of which is of
            type 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 provide
            additional checking of values, etc.  Here, we want the count
            element always to be nonnegative, so we redefine the count
            accessor 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.



















3rd Berkeley Distribution    perl 5.005, patch 02             Class::Struct(3)