lib/Class/Struct.pm

package Class::Struct;

## See POD after __END__

use 5.006_001;

use strict;
use warnings::register;
our(@ISA, @EXPORT, $VERSION);

use Carp;

require Exporter;
@ISA = qw(Exporter);
@EXPORT = qw(struct);

$VERSION = '0.63';

## Tested on 5.002 and 5.003 without class membership tests:
my $CHECK_CLASS_MEMBERSHIP = ($] >= 5.003_95);

my $print = 0;
sub printem {
    if (@_) { $print = shift }
    else    { $print++ }
}

{
    package Class::Struct::Tie_ISA;

    sub TIEARRAY {
        my $class = shift;
        return bless [], $class;
    }

    sub STORE {
        my ($self, $index, $value) = @_;
        Class::Struct::_subclass_error();
    }

    sub FETCH {
        my ($self, $index) = @_;
        $self->[$index];
    }

    sub FETCHSIZE {
        my $self = shift;
        return scalar(@$self);
    }

    sub DESTROY { }
}

sub import {
    my $self = shift;

    if ( @_ == 0 ) {
      $self->export_to_level( 1, $self, @EXPORT );
    } elsif ( @_ == 1 ) {
        # This is admittedly a little bit silly:
        # do we ever export anything else than 'struct'...?
      $self->export_to_level( 1, $self, @_ );
    } else {
      goto &struct;
    }
}

sub struct {

    # Determine parameter list structure, one of:
    #   struct( class => [ element-list ])
    #   struct( class => { element-list })
    #   struct( element-list )
    # Latter form assumes current package name as struct name.

    my ($class, @decls);
    my $base_type = ref $_[1];
    if ( $base_type eq 'HASH' ) {
        $class = shift;
        @decls = %{shift()};
        _usage_error() if @_;
    }
    elsif ( $base_type eq 'ARRAY' ) {
        $class = shift;
        @decls = @{shift()};
        _usage_error() if @_;
    }
    else {
        $base_type = 'ARRAY';
        $class = (caller())[0];
        @decls = @_;
    }

    _usage_error() if @decls % 2 == 1;

    # Ensure we are not, and will not be, a subclass.

    my $isa = do {
        no strict 'refs';
        \@{$class . '::ISA'};
    };
    _subclass_error() if @$isa;
    tie @$isa, 'Class::Struct::Tie_ISA';

    # Create constructor.

    croak "function 'new' already defined in package $class"
        if do { no strict 'refs'; defined &{$class . "::new"} };

    my @methods = ();
    my %refs = ();
    my %arrays = ();
    my %hashes = ();
    my %classes = ();
    my $got_class = 0;
    my $out = '';

    $out = "{\n  package $class;\n  use Carp;\n  sub new {\n";
    $out .= "    my (\$class, \%init) = \@_;\n";
    $out .= "    \$class = __PACKAGE__ unless \@_;\n";

    my $cnt = 0;
    my $idx = 0;
    my( $cmt, $name, $type, $elem );

    if( $base_type eq 'HASH' ){
        $out .= "    my(\$r) = {};\n";
        $cmt = '';
    }
    elsif( $base_type eq 'ARRAY' ){
        $out .= "    my(\$r) = [];\n";
    }
    while( $idx < @decls ){
        $name = $decls[$idx];
        $type = $decls[$idx+1];
        push( @methods, $name );
        if( $base_type eq 'HASH' ){
            $elem = "{'${class}::$name'}";
        }
        elsif( $base_type eq 'ARRAY' ){
            $elem = "[$cnt]";
            ++$cnt;
            $cmt = " # $name";
        }
        if( $type =~ /^\*(.)/ ){
            $refs{$name}++;
            $type = $1;
        }
        my $init = "defined(\$init{'$name'}) ? \$init{'$name'} :";
        if( $type eq '@' ){
            $out .= "    croak 'Initializer for $name must be array reference'\n"; 
            $out .= "        if defined(\$init{'$name'}) && ref(\$init{'$name'}) ne 'ARRAY';\n";
            $out .= "    \$r->$elem = $init [];$cmt\n"; 
            $arrays{$name}++;
        }
        elsif( $type eq '%' ){
            $out .= "    croak 'Initializer for $name must be hash reference'\n";
            $out .= "        if defined(\$init{'$name'}) && ref(\$init{'$name'}) ne 'HASH';\n";
            $out .= "    \$r->$elem = $init {};$cmt\n";
            $hashes{$name}++;
        }
        elsif ( $type eq '$') {
            $out .= "    \$r->$elem = $init undef;$cmt\n";
        }
        elsif( $type =~ /^\w+(?:::\w+)*$/ ){
            $out .= "    if (defined(\$init{'$name'})) {\n";
           $out .= "       if (ref \$init{'$name'} eq 'HASH')\n";
            $out .= "            { \$r->$elem = $type->new(\%{\$init{'$name'}}) } $cmt\n";
           $out .= "       elsif (UNIVERSAL::isa(\$init{'$name'}, '$type'))\n";
            $out .= "            { \$r->$elem = \$init{'$name'} } $cmt\n";
            $out .= "       else { croak 'Initializer for $name must be hash or $type reference' }\n";
            $out .= "    }\n";
            $classes{$name} = $type;
            $got_class = 1;
        }
        else{
            croak "'$type' is not a valid struct element type";
        }
        $idx += 2;
    }
    $out .= "    bless \$r, \$class;\n  }\n";

    # Create accessor methods.

    my( $pre, $pst, $sel );
    $cnt = 0;
    foreach $name (@methods){
        if ( do { no strict 'refs'; defined &{$class . "::$name"} } ) {
            warnings::warnif("function '$name' already defined, overrides struct accessor method");
        }
        else {
            $pre = $pst = $cmt = $sel = '';
            if( defined $refs{$name} ){
                $pre = "\\(";
                $pst = ")";
                $cmt = " # returns ref";
            }
            $out .= "  sub $name {$cmt\n    my \$r = shift;\n";
            if( $base_type eq 'ARRAY' ){
                $elem = "[$cnt]";
                ++$cnt;
            }
            elsif( $base_type eq 'HASH' ){
                $elem = "{'${class}::$name'}";
            }
            if( defined $arrays{$name} ){
                $out .= "    my \$i;\n";
                $out .= "    \@_ ? (\$i = shift) : return \$r->$elem;\n"; 
                $out .= "    if (ref(\$i) eq 'ARRAY' && !\@_) { \$r->$elem = \$i; return \$r }\n";
                $sel = "->[\$i]";
            }
            elsif( defined $hashes{$name} ){
                $out .= "    my \$i;\n";
                $out .= "    \@_ ? (\$i = shift) : return \$r->$elem;\n";
                $out .= "    if (ref(\$i) eq 'HASH' && !\@_) { \$r->$elem = \$i; return \$r }\n";
                $sel = "->{\$i}";
            }
            elsif( defined $classes{$name} ){
                if ( $CHECK_CLASS_MEMBERSHIP ) {
                    $out .= "    croak '$name argument is wrong class' if \@_ && ! UNIVERSAL::isa(\$_[0], '$classes{$name}');\n";
                }
            }
            $out .= "    croak 'Too many args to $name' if \@_ > 1;\n";
            $out .= "    \@_ ? ($pre\$r->$elem$sel = shift$pst) : $pre\$r->$elem$sel$pst;\n";
            $out .= "  }\n";
        }
    }
    $out .= "}\n1;\n";

    print $out if $print;
    my $result = eval $out;
    carp $@ if $@;
}

sub _usage_error {
    confess "struct usage error";
}

sub _subclass_error {
    croak 'struct class cannot be a subclass (@ISA not allowed)';
}

1; # for require


__END__

=head1 NAME

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

=head1 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, ... );

    # Declare struct at compile time
    use Class::Struct CLASS_NAME => [ ELEMENT_NAME => ELEMENT_TYPE, ... ];
    use Class::Struct CLASS_NAME => { ELEMENT_NAME => ELEMENT_TYPE, ... };

    # declare struct at compile time, based on array, implicit class name:
    package CLASS_NAME;
    use Class::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

=head1 DESCRIPTION

C<Class::Struct> exports a single function, C<struct>.
Given a list of element names and types, and optionally
a class name, C<struct> creates a Perl 5 class that implements
a "struct-like" data structure.

The new class is given a constructor method, C<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 C<sub> of the
same name in the package.  (See Example 2.)

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

=head2 The C<struct()> function

The C<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 C<struct> must not be a subclass of another
class other than C<UNIVERSAL>.

It can, however, be used as a superclass for other classes. To facilitate
this, the generated constructor method uses a two-argument blessing.
Furthermore, if the class is hash-based, the key of each element is
prefixed with the class name (see I<Perl Cookbook>, Recipe 13.12).

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

The I<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 (B<-w>) is set.

=head2 Class Creation at Compile Time

C<Class::Struct> can create your class at compile time.  The main reason
for doing this is obvious, so your class acts like every other class in
Perl.  Creating your class at compile time will make the order of events
similar to using any other class ( or Perl module ).

There is no significant speed gain between compile time and run time
class creation, there is just a new, more standard order of events.

=head2 Element Types and Accessor Methods

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

The accessor method provided by C<struct> for an element depends
on the declared type of the element.

=over 4

=item Scalar (C<'$'> or C<'*$'>)

The element is a scalar, and by default is initialized to C<undef>
(but see L<Initializing with new>).

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

If the element type is C<'$'>, the value of the element (after
assignment) is returned. If the element type is C<'*$'>, a reference
to the element is returned.

=item Array (C<'@'> or C<'*@'>)

The element is an array, initialized by default to C<()>.

With no argument, the accessor returns a reference to the
element's whole array (whether or not the element was
specified as C<'@'> or C<'*@'>).

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

As a special case, when the accessor is called with an array reference
as the sole argument, this causes an assignment of the whole array element.
The object reference is returned.

=item Hash (C<'%'> or C<'*%'>)

The element is a hash, initialized by default to C<()>.

With no argument, the accessor returns a reference to the
element's whole hash (whether or not the element was
specified as C<'%'> or C<'*%'>).

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 C<'%'>, the
accessor returns the hash element value.  If the element type is
C<'*%'>, a reference to the hash element is returned.

As a special case, when the accessor is called with a hash reference
as the sole argument, this causes an assignment of the whole hash element.
The object reference is returned.

=item Class (C<'Class_Name'> or C<'*Class_Name'>)

The element's value must be a reference blessed to the named
class or to one of its subclasses. The element is not initialized
by default.

The accessor's argument, if any, is assigned to the element. The
accessor will C<croak> if this is not an appropriate object
reference.

If the element type does not start with a C<'*'>, the accessor
returns the element value (after assignment). If the element type
starts with a C<'*'>, a reference to the element itself is returned.

=back

=head2 Initializing with C<new>

C<struct> always creates a constructor called C<new>. That constructor
may take a list of initializers for the various elements of the new
struct. 

Each initializer is a pair of values: I<element name>C< =E<gt> >I<value>.
The initializer value for a scalar element is just a scalar value. The 
initializer for an array element is an array reference. The initializer
for a hash is a hash reference.

The initializer for a class element is an object of the corresponding class,
or of one of it's subclasses, or a reference to a hash containing named 
arguments to be passed to the element's constructor.

See Example 3 below for an example of initialization.

=head1 EXAMPLES

=over 4

=item Example 1

Giving a struct element a class type that is also a struct is how
structs are nested.  Here, C<Timeval> represents a time (seconds and
microseconds), and C<Rusage> has two elements, each of which is of
type C<Timeval>.

    use Class::Struct;

    struct( Rusage => {
        ru_utime => 'Timeval',  # user time used
        ru_stime => 'Timeval',  # system time used
    });

    struct( Timeval => [
        tv_secs  => '$',        # seconds
        tv_usecs => '$',        # microseconds
    ]);

        # create an object:
    my $t = Rusage->new(ru_utime=>Timeval->new(), ru_stime=>Timeval->new());

        # $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);

=item Example 2

An accessor function can be redefined in order to provide
additional checking of values, etc.  Here, we want the C<count>
element always to be nonnegative, so we redefine the C<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->{'MyObj::count'} = shift;
            warn "Too many args to count" if @_;
        }
        return $self->{'MyObj::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!

=item Example 3

The constructor of a generated class can be passed a list
of I<element>=>I<value> pairs, with which to initialize the struct.
If no initializer is specified for a particular element, its default
initialization is performed instead. Initializers for non-existent
elements are silently ignored.

Note that the initializer for a nested class may be specified as
an object of that class, or as a reference to a hash of initializers
that are passed on to the nested struct's constructor.

    use Class::Struct;

    struct Breed =>
    {
        name  => '$',
        cross => '$',
    };

    struct Cat =>
    [
        name     => '$',
        kittens  => '@',
        markings => '%',
        breed    => 'Breed',
    ];


    my $cat = Cat->new( name     => 'Socks',
                        kittens  => ['Monica', 'Kenneth'],
                        markings => { socks=>1, blaze=>"white" },
                        breed    => Breed->new(name=>'short-hair', cross=>1),
                   or:  breed    => {name=>'short-hair', cross=>1},
                      );

    print "Once a cat called ", $cat->name, "\n";
    print "(which was a ", $cat->breed->name, ")\n";
    print "had two kittens: ", join(' and ', @{$cat->kittens}), "\n";

=back

=head1 Author and Modification History

Modified by Damian Conway, 2001-09-10, v0.62.

   Modified implicit construction of nested objects.
   Now will also take an object ref instead of requiring a hash ref.
   Also default initializes nested object attributes to undef, rather
   than calling object constructor without args
   Original over-helpfulness was fraught with problems:
       * the class's constructor might not be called 'new'
       * the class might not have a hash-like-arguments constructor
       * the class might not have a no-argument constructor
       * "recursive" data structures didn't work well:
                 package Person;
                 struct { mother => 'Person', father => 'Person'};


Modified by Casey West, 2000-11-08, v0.59.

    Added the ability for compile time class creation.

Modified by Damian Conway, 1999-03-05, v0.58.

    Added handling of hash-like arg list to class ctor.

    Changed to two-argument blessing in ctor to support
    derivation from created classes.

    Added classname prefixes to keys in hash-based classes
    (refer to "Perl Cookbook", Recipe 13.12 for rationale).

    Corrected behaviour of accessors for '*@' and '*%' struct
    elements.  Package now implements documented behaviour when
    returning a reference to an entire hash or array element.
    Previously these were returned as a reference to a reference
    to the element.

Renamed to C<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 C<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.

=cut
Revision:	1.1
Committed:	Thu Jun 30 14:27:10 2005 UTC (21 years, 3 months ago) by root
Branch:	MAIN
CVS Tags:	PERL-5-8-7, HEAD
Branch point for:	PERL
Log Message:	* empty log message *
#	User	Rev	Content
1	root	1.1	package Class::Struct;
2
3			## See POD after __END__
4
5			use 5.006_001;
6
7			use strict;
8			use warnings::register;
9			our(@ISA, @EXPORT, $VERSION);
10
11			use Carp;
12
13			require Exporter;
14			@ISA = qw(Exporter);
15			@EXPORT = qw(struct);
16
17			$VERSION = '0.63';
18
19			## Tested on 5.002 and 5.003 without class membership tests:
20			my $CHECK_CLASS_MEMBERSHIP = ($] >= 5.003_95);
21
22			my $print = 0;
23			sub printem {
24			if (@_) { $print = shift }
25			else { $print++ }
26			}
27
28			{
29			package Class::Struct::Tie_ISA;
30
31			sub TIEARRAY {
32			my $class = shift;
33			return bless [], $class;
34			}
35
36			sub STORE {
37			my ($self, $index, $value) = @_;
38			Class::Struct::_subclass_error();
39			}
40
41			sub FETCH {
42			my ($self, $index) = @_;
43			$self->[$index];
44			}
45
46			sub FETCHSIZE {
47			my $self = shift;
48			return scalar(@$self);
49			}
50
51			sub DESTROY { }
52			}
53
54			sub import {
55			my $self = shift;
56
57			if ( @_ == 0 ) {
58			$self->export_to_level( 1, $self, @EXPORT );
59			} elsif ( @_ == 1 ) {
60			# This is admittedly a little bit silly:
61			# do we ever export anything else than 'struct'...?
62			$self->export_to_level( 1, $self, @_ );
63			} else {
64			goto &struct;
65			}
66			}
67
68			sub struct {
69
70			# Determine parameter list structure, one of:
71			# struct( class => [ element-list ])
72			# struct( class => { element-list })
73			# struct( element-list )
74			# Latter form assumes current package name as struct name.
75
76			my ($class, @decls);
77			my $base_type = ref $_[1];
78			if ( $base_type eq 'HASH' ) {
79			$class = shift;
80			@decls = %{shift()};
81			_usage_error() if @_;
82			}
83			elsif ( $base_type eq 'ARRAY' ) {
84			$class = shift;
85			@decls = @{shift()};
86			_usage_error() if @_;
87			}
88			else {
89			$base_type = 'ARRAY';
90			$class = (caller())[0];
91			@decls = @_;
92			}
93
94			_usage_error() if @decls % 2 == 1;
95
96			# Ensure we are not, and will not be, a subclass.
97
98			my $isa = do {
99			no strict 'refs';
100			\@{$class . '::ISA'};
101			};
102			_subclass_error() if @$isa;
103			tie @$isa, 'Class::Struct::Tie_ISA';
104
105			# Create constructor.
106
107			croak "function 'new' already defined in package $class"
108			if do { no strict 'refs'; defined &{$class . "::new"} };
109
110			my @methods = ();
111			my %refs = ();
112			my %arrays = ();
113			my %hashes = ();
114			my %classes = ();
115			my $got_class = 0;
116			my $out = '';
117
118			$out = "{\n package $class;\n use Carp;\n sub new {\n";
119			$out .= " my (\$class, \%init) = \@_;\n";
120			$out .= " \$class = __PACKAGE__ unless \@_;\n";
121
122			my $cnt = 0;
123			my $idx = 0;
124			my( $cmt, $name, $type, $elem );
125
126			if( $base_type eq 'HASH' ){
127			$out .= " my(\$r) = {};\n";
128			$cmt = '';
129			}
130			elsif( $base_type eq 'ARRAY' ){
131			$out .= " my(\$r) = [];\n";
132			}
133			while( $idx < @decls ){
134			$name = $decls[$idx];
135			$type = $decls[$idx+1];
136			push( @methods, $name );
137			if( $base_type eq 'HASH' ){
138			$elem = "{'${class}::$name'}";
139			}
140			elsif( $base_type eq 'ARRAY' ){
141			$elem = "[$cnt]";
142			++$cnt;
143			$cmt = " # $name";
144			}
145			if( $type =~ /^\*(.)/ ){
146			$refs{$name}++;
147			$type = $1;
148			}
149			my $init = "defined(\$init{'$name'}) ? \$init{'$name'} :";
150			if( $type eq '@' ){
151			$out .= " croak 'Initializer for $name must be array reference'\n";
152			$out .= " if defined(\$init{'$name'}) && ref(\$init{'$name'}) ne 'ARRAY';\n";
153			$out .= " \$r->$elem = $init [];$cmt\n";
154			$arrays{$name}++;
155			}
156			elsif( $type eq '%' ){
157			$out .= " croak 'Initializer for $name must be hash reference'\n";
158			$out .= " if defined(\$init{'$name'}) && ref(\$init{'$name'}) ne 'HASH';\n";
159			$out .= " \$r->$elem = $init {};$cmt\n";
160			$hashes{$name}++;
161			}
162			elsif ( $type eq '$') {
163			$out .= " \$r->$elem = $init undef;$cmt\n";
164			}
165			elsif( $type =~ /^\w+(?:::\w+)*$/ ){
166			$out .= " if (defined(\$init{'$name'})) {\n";
167			$out .= " if (ref \$init{'$name'} eq 'HASH')\n";
168			$out .= " { \$r->$elem = $type->new(\%{\$init{'$name'}}) } $cmt\n";
169			$out .= " elsif (UNIVERSAL::isa(\$init{'$name'}, '$type'))\n";
170			$out .= " { \$r->$elem = \$init{'$name'} } $cmt\n";
171			$out .= " else { croak 'Initializer for $name must be hash or $type reference' }\n";
172			$out .= " }\n";
173			$classes{$name} = $type;
174			$got_class = 1;
175			}
176			else{
177			croak "'$type' is not a valid struct element type";
178			}
179			$idx += 2;
180			}
181			$out .= " bless \$r, \$class;\n }\n";
182
183			# Create accessor methods.
184
185			my( $pre, $pst, $sel );
186			$cnt = 0;
187			foreach $name (@methods){
188			if ( do { no strict 'refs'; defined &{$class . "::$name"} } ) {
189			warnings::warnif("function '$name' already defined, overrides struct accessor method");
190			}
191			else {
192			$pre = $pst = $cmt = $sel = '';
193			if( defined $refs{$name} ){
194			$pre = "\\(";
195			$pst = ")";
196			$cmt = " # returns ref";
197			}
198			$out .= " sub $name {$cmt\n my \$r = shift;\n";
199			if( $base_type eq 'ARRAY' ){
200			$elem = "[$cnt]";
201			++$cnt;
202			}
203			elsif( $base_type eq 'HASH' ){
204			$elem = "{'${class}::$name'}";
205			}
206			if( defined $arrays{$name} ){
207			$out .= " my \$i;\n";
208			$out .= " \@_ ? (\$i = shift) : return \$r->$elem;\n";
209			$out .= " if (ref(\$i) eq 'ARRAY' && !\@_) { \$r->$elem = \$i; return \$r }\n";
210			$sel = "->[\$i]";
211			}
212			elsif( defined $hashes{$name} ){
213			$out .= " my \$i;\n";
214			$out .= " \@_ ? (\$i = shift) : return \$r->$elem;\n";
215			$out .= " if (ref(\$i) eq 'HASH' && !\@_) { \$r->$elem = \$i; return \$r }\n";
216			$sel = "->{\$i}";
217			}
218			elsif( defined $classes{$name} ){
219			if ( $CHECK_CLASS_MEMBERSHIP ) {
220			$out .= " croak '$name argument is wrong class' if \@_ && ! UNIVERSAL::isa(\$_[0], '$classes{$name}');\n";
221			}
222			}
223			$out .= " croak 'Too many args to $name' if \@_ > 1;\n";
224			$out .= " \@_ ? ($pre\$r->$elem$sel = shift$pst) : $pre\$r->$elem$sel$pst;\n";
225			$out .= " }\n";
226			}
227			}
228			$out .= "}\n1;\n";
229
230			print $out if $print;
231			my $result = eval $out;
232			carp $@ if $@;
233			}
234
235			sub _usage_error {
236			confess "struct usage error";
237			}
238
239			sub _subclass_error {
240			croak 'struct class cannot be a subclass (@ISA not allowed)';
241			}
242
243			1; # for require
244
245
246			__END__
247
248			=head1 NAME
249
250			Class::Struct - declare struct-like datatypes as Perl classes
251
252			=head1 SYNOPSIS
253
254			use Class::Struct;
255			# declare struct, based on array:
256			struct( CLASS_NAME => [ ELEMENT_NAME => ELEMENT_TYPE, ... ]);
257			# declare struct, based on hash:
258			struct( CLASS_NAME => { ELEMENT_NAME => ELEMENT_TYPE, ... });
259
260			package CLASS_NAME;
261			use Class::Struct;
262			# declare struct, based on array, implicit class name:
263			struct( ELEMENT_NAME => ELEMENT_TYPE, ... );
264
265			# Declare struct at compile time
266			use Class::Struct CLASS_NAME => [ ELEMENT_NAME => ELEMENT_TYPE, ... ];
267			use Class::Struct CLASS_NAME => { ELEMENT_NAME => ELEMENT_TYPE, ... };
268
269			# declare struct at compile time, based on array, implicit class name:
270			package CLASS_NAME;
271			use Class::Struct ELEMENT_NAME => ELEMENT_TYPE, ... ;
272
273			package Myobj;
274			use Class::Struct;
275			# declare struct with four types of elements:
276			struct( s => '$', a => '@', h => '%', c => 'My_Other_Class' );
277
278			$obj = new Myobj; # constructor
279
280			# scalar type accessor:
281			$element_value = $obj->s; # element value
282			$obj->s('new value'); # assign to element
283
284			# array type accessor:
285			$ary_ref = $obj->a; # reference to whole array
286			$ary_element_value = $obj->a(2); # array element value
287			$obj->a(2, 'new value'); # assign to array element
288
289			# hash type accessor:
290			$hash_ref = $obj->h; # reference to whole hash
291			$hash_element_value = $obj->h('x'); # hash element value
292			$obj->h('x', 'new value'); # assign to hash element
293
294			# class type accessor:
295			$element_value = $obj->c; # object reference
296			$obj->c->method(...); # call method of object
297			$obj->c(new My_Other_Class); # assign a new object
298
299			=head1 DESCRIPTION
300
301			C<Class::Struct> exports a single function, C<struct>.
302			Given a list of element names and types, and optionally
303			a class name, C<struct> creates a Perl 5 class that implements
304			a "struct-like" data structure.
305
306			The new class is given a constructor method, C<new>, for creating
307			struct objects.
308
309			Each element in the struct data has an accessor method, which is
310			used to assign to the element and to fetch its value. The
311			default accessor can be overridden by declaring a C<sub> of the
312			same name in the package. (See Example 2.)
313
314			Each element's type can be scalar, array, hash, or class.
315
316			=head2 The C<struct()> function
317
318			The C<struct> function has three forms of parameter-list.
319
320			struct( CLASS_NAME => [ ELEMENT_LIST ]);
321			struct( CLASS_NAME => { ELEMENT_LIST });
322			struct( ELEMENT_LIST );
323
324			The first and second forms explicitly identify the name of the
325			class being created. The third form assumes the current package
326			name as the class name.
327
328			An object of a class created by the first and third forms is
329			based on an array, whereas an object of a class created by the
330			second form is based on a hash. The array-based forms will be
331			somewhat faster and smaller; the hash-based forms are more
332			flexible.
333
334			The class created by C<struct> must not be a subclass of another
335			class other than C<UNIVERSAL>.
336
337			It can, however, be used as a superclass for other classes. To facilitate
338			this, the generated constructor method uses a two-argument blessing.
339			Furthermore, if the class is hash-based, the key of each element is
340			prefixed with the class name (see I<Perl Cookbook>, Recipe 13.12).
341
342			A function named C<new> must not be explicitly defined in a class
343			created by C<struct>.
344
345			The I<ELEMENT_LIST> has the form
346
347			NAME => TYPE, ...
348
349			Each name-type pair declares one element of the struct. Each
350			element name will be defined as an accessor method unless a
351			method by that name is explicitly defined; in the latter case, a
352			warning is issued if the warning flag (B<-w>) is set.
353
354			=head2 Class Creation at Compile Time
355
356			C<Class::Struct> can create your class at compile time. The main reason
357			for doing this is obvious, so your class acts like every other class in
358			Perl. Creating your class at compile time will make the order of events
359			similar to using any other class ( or Perl module ).
360
361			There is no significant speed gain between compile time and run time
362			class creation, there is just a new, more standard order of events.
363
364			=head2 Element Types and Accessor Methods
365
366			The four element types -- scalar, array, hash, and class -- are
367			represented by strings -- C<'$'>, C<'@'>, C<'%'>, and a class name --
368			optionally preceded by a C<'*'>.
369
370			The accessor method provided by C<struct> for an element depends
371			on the declared type of the element.
372
373			=over 4
374
375			=item Scalar (C<'$'> or C<'*$'>)
376
377			The element is a scalar, and by default is initialized to C<undef>
378			(but see L<Initializing with new>).
379
380			The accessor's argument, if any, is assigned to the element.
381
382			If the element type is C<'$'>, the value of the element (after
383			assignment) is returned. If the element type is C<'*$'>, a reference
384			to the element is returned.
385
386			=item Array (C<'@'> or C<'*@'>)
387
388			The element is an array, initialized by default to C<()>.
389
390			With no argument, the accessor returns a reference to the
391			element's whole array (whether or not the element was
392			specified as C<'@'> or C<'*@'>).
393
394			With one or two arguments, the first argument is an index
395			specifying one element of the array; the second argument, if
396			present, is assigned to the array element. If the element type
397			is C<'@'>, the accessor returns the array element value. If the
398			element type is C<'*@'>, a reference to the array element is
399			returned.
400
401			As a special case, when the accessor is called with an array reference
402			as the sole argument, this causes an assignment of the whole array element.
403			The object reference is returned.
404
405			=item Hash (C<'%'> or C<'*%'>)
406
407			The element is a hash, initialized by default to C<()>.
408
409			With no argument, the accessor returns a reference to the
410			element's whole hash (whether or not the element was
411			specified as C<'%'> or C<'*%'>).
412
413			With one or two arguments, the first argument is a key specifying
414			one element of the hash; the second argument, if present, is
415			assigned to the hash element. If the element type is C<'%'>, the
416			accessor returns the hash element value. If the element type is
417			C<'*%'>, a reference to the hash element is returned.
418
419			As a special case, when the accessor is called with a hash reference
420			as the sole argument, this causes an assignment of the whole hash element.
421			The object reference is returned.
422
423			=item Class (C<'Class_Name'> or C<'*Class_Name'>)
424
425			The element's value must be a reference blessed to the named
426			class or to one of its subclasses. The element is not initialized
427			by default.
428
429			The accessor's argument, if any, is assigned to the element. The
430			accessor will C<croak> if this is not an appropriate object
431			reference.
432
433			If the element type does not start with a C<'*'>, the accessor
434			returns the element value (after assignment). If the element type
435			starts with a C<'*'>, a reference to the element itself is returned.
436
437			=back
438
439			=head2 Initializing with C<new>
440
441			C<struct> always creates a constructor called C<new>. That constructor
442			may take a list of initializers for the various elements of the new
443			struct.
444
445			Each initializer is a pair of values: I<element name>C< =E<gt> >I<value>.
446			The initializer value for a scalar element is just a scalar value. The
447			initializer for an array element is an array reference. The initializer
448			for a hash is a hash reference.
449
450			The initializer for a class element is an object of the corresponding class,
451			or of one of it's subclasses, or a reference to a hash containing named
452			arguments to be passed to the element's constructor.
453
454			See Example 3 below for an example of initialization.
455
456			=head1 EXAMPLES
457
458			=over 4
459
460			=item Example 1
461
462			Giving a struct element a class type that is also a struct is how
463			structs are nested. Here, C<Timeval> represents a time (seconds and
464			microseconds), and C<Rusage> has two elements, each of which is of
465			type C<Timeval>.
466
467			use Class::Struct;
468
469			struct( Rusage => {
470			ru_utime => 'Timeval', # user time used
471			ru_stime => 'Timeval', # system time used
472			});
473
474			struct( Timeval => [
475			tv_secs => '$', # seconds
476			tv_usecs => '$', # microseconds
477			]);
478
479			# create an object:
480			my $t = Rusage->new(ru_utime=>Timeval->new(), ru_stime=>Timeval->new());
481
482			# $t->ru_utime and $t->ru_stime are objects of type Timeval.
483			# set $t->ru_utime to 100.0 sec and $t->ru_stime to 5.0 sec.
484			$t->ru_utime->tv_secs(100);
485			$t->ru_utime->tv_usecs(0);
486			$t->ru_stime->tv_secs(5);
487			$t->ru_stime->tv_usecs(0);
488
489			=item Example 2
490
491			An accessor function can be redefined in order to provide
492			additional checking of values, etc. Here, we want the C<count>
493			element always to be nonnegative, so we redefine the C<count>
494			accessor accordingly.
495
496			package MyObj;
497			use Class::Struct;
498
499			# declare the struct
500			struct ( 'MyObj', { count => '$', stuff => '%' } );
501
502			# override the default accessor method for 'count'
503			sub count {
504			my $self = shift;
505			if ( @_ ) {
506			die 'count must be nonnegative' if $_[0] < 0;
507			$self->{'MyObj::count'} = shift;
508			warn "Too many args to count" if @_;
509			}
510			return $self->{'MyObj::count'};
511			}
512
513			package main;
514			$x = new MyObj;
515			print "\$x->count(5) = ", $x->count(5), "\n";
516			# prints '$x->count(5) = 5'
517
518			print "\$x->count = ", $x->count, "\n";
519			# prints '$x->count = 5'
520
521			print "\$x->count(-5) = ", $x->count(-5), "\n";
522			# dies due to negative argument!
523
524			=item Example 3
525
526			The constructor of a generated class can be passed a list
527			of I<element>=>I<value> pairs, with which to initialize the struct.
528			If no initializer is specified for a particular element, its default
529			initialization is performed instead. Initializers for non-existent
530			elements are silently ignored.
531
532			Note that the initializer for a nested class may be specified as
533			an object of that class, or as a reference to a hash of initializers
534			that are passed on to the nested struct's constructor.
535
536			use Class::Struct;
537
538			struct Breed =>
539			{
540			name => '$',
541			cross => '$',
542			};
543
544			struct Cat =>
545			[
546			name => '$',
547			kittens => '@',
548			markings => '%',
549			breed => 'Breed',
550			];
551
552
553			my $cat = Cat->new( name => 'Socks',
554			kittens => ['Monica', 'Kenneth'],
555			markings => { socks=>1, blaze=>"white" },
556			breed => Breed->new(name=>'short-hair', cross=>1),
557			or: breed => {name=>'short-hair', cross=>1},
558			);
559
560			print "Once a cat called ", $cat->name, "\n";
561			print "(which was a ", $cat->breed->name, ")\n";
562			print "had two kittens: ", join(' and ', @{$cat->kittens}), "\n";
563
564			=back
565
566			=head1 Author and Modification History
567
568			Modified by Damian Conway, 2001-09-10, v0.62.
569
570			Modified implicit construction of nested objects.
571			Now will also take an object ref instead of requiring a hash ref.
572			Also default initializes nested object attributes to undef, rather
573			than calling object constructor without args
574			Original over-helpfulness was fraught with problems:
575			* the class's constructor might not be called 'new'
576			* the class might not have a hash-like-arguments constructor
577			* the class might not have a no-argument constructor
578			* "recursive" data structures didn't work well:
579			package Person;
580			struct { mother => 'Person', father => 'Person'};
581
582
583			Modified by Casey West, 2000-11-08, v0.59.
584
585			Added the ability for compile time class creation.
586
587			Modified by Damian Conway, 1999-03-05, v0.58.
588
589			Added handling of hash-like arg list to class ctor.
590
591			Changed to two-argument blessing in ctor to support
592			derivation from created classes.
593
594			Added classname prefixes to keys in hash-based classes
595			(refer to "Perl Cookbook", Recipe 13.12 for rationale).
596
597			Corrected behaviour of accessors for '@' and '%' struct
598			elements. Package now implements documented behaviour when
599			returning a reference to an entire hash or array element.
600			Previously these were returned as a reference to a reference
601			to the element.
602
603			Renamed to C<Class::Struct> and modified by Jim Miner, 1997-04-02.
604
605			members() function removed.
606			Documentation corrected and extended.
607			Use of struct() in a subclass prohibited.
608			User definition of accessor allowed.
609			Treatment of '*' in element types corrected.
610			Treatment of classes as element types corrected.
611			Class name to struct() made optional.
612			Diagnostic checks added.
613
614			Originally C<Class::Template> by Dean Roehrich.
615
616			# Template.pm --- struct/member template builder
617			# 12mar95
618			# Dean Roehrich
619			#
620			# changes/bugs fixed since 28nov94 version:
621			# - podified
622			# changes/bugs fixed since 21nov94 version:
623			# - Fixed examples.
624			# changes/bugs fixed since 02sep94 version:
625			# - Moved to Class::Template.
626			# changes/bugs fixed since 20feb94 version:
627			# - Updated to be a more proper module.
628			# - Added "use strict".
629			# - Bug in build_methods, was using @var when @$var needed.
630			# - Now using my() rather than local().
631			#
632			# Uses perl5 classes to create nested data types.
633			# This is offered as one implementation of Tom Christiansen's "structs.pl"
634			# idea.
635
636			=cut