[p5sagit/p5-mst-13.2.git] / lib / Class / Struct.pm

package Class::Struct;

## See POD after __END__

use 5.005_64;

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

use Carp;

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

$VERSION = '0.59';

## 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 {
      &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( $type =~ /^\w+(?:::\w+)*$/ ){
            $init = "defined(\$init{'$name'}) ? \%{\$init{'$name'}} : ()";
            $out .= "    croak 'Initializer for $name must be hash reference'\n";
            $out .= "        if defined(\$init{'$name'}) && ref(\$init{'$name'}) ne 'HASH';\n";
            $out .= "    \$r->$elem = '${type}'->new($init);$cmt\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"; 
                $sel = "->[\$i]";
            }
            elsif( defined $hashes{$name} ){
                $out .= "    my \$i;\n";
                $out .= "    \@_ ? (\$i = shift) : return \$r->$elem;\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, ... };

    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

=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.

=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.

=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 initialized to
the result of calling the C<new> constructor of the named class.

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 also a hash reference, and the
contents of that hash are passed to the element's own constructor.

See Example 3 below for an example of initialization.

=head1 EXAMPLES

=over

=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,  # 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);

=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->{'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!

=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 struct is specified
as an anonymous hash of initializers, which is 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    => { 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 Casey Tweten, 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
Commit	Line	Data
8cc95fdb	1	package Class::Struct;
	2
	3	## See POD after __END__
	4
cb50131a	5	use 5.005_64;
8cc95fdb	6
8cc95fdb	7	use strict;
ee8c7f54	8	use warnings::register;
cb50131a	9	our(@ISA, @EXPORT, $VERSION);
8cc95fdb	10
	11	use Carp;
	12
	13	require Exporter;
	14	@ISA = qw(Exporter);
	15	@EXPORT = qw(struct);
	16
0e06870b	17	$VERSION = '0.59';
430530ea	18
8cc95fdb	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
f740b751	46	sub FETCHSIZE {
	47	my $self = shift;
	48	return scalar(@$self);
	49	}
	50
8cc95fdb	51	sub DESTROY { }
	52	}
	53
0e06870b	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, $self, @_ );
	63	} else {
	64	&struct;
	65	}
	66	}
	67
8cc95fdb	68	sub struct {
	69
	70	# Determine parameter list structure, one of:
	71	# struct( class => [ element-list ])
	72	# struct( class => { element-list })
	73	# struct( element-list )
	74	# Latter form assumes current package name as struct name.
	75
	76	my ($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	}
0e06870b	93
8cc95fdb	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";
430530ea	119	$out .= " my (\$class, \%init) = \@_;\n";
f01e5ef6	120	$out .= " \$class = __PACKAGE__ unless \@_;\n";
8cc95fdb	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' ){
430530ea	138	$elem = "{'${class}::$name'}";
8cc95fdb	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	}
430530ea	149	my $init = "defined(\$init{'$name'}) ? \$init{'$name'} :";
8cc95fdb	150	if( $type eq '@' ){
430530ea	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";
8cc95fdb	154	$arrays{$name}++;
	155	}
	156	elsif( $type eq '%' ){
430530ea	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";
8cc95fdb	160	$hashes{$name}++;
	161	}
	162	elsif ( $type eq '$') {
430530ea	163	$out .= " \$r->$elem = $init undef;$cmt\n";
8cc95fdb	164	}
8cc95fdb	165	elsif( $type =~ /^\w+(?:::\w+)*$/ ){
430530ea	166	$init = "defined(\$init{'$name'}) ? \%{\$init{'$name'}} : ()";
	167	$out .= " croak 'Initializer for $name must be hash reference'\n";
	168	$out .= " if defined(\$init{'$name'}) && ref(\$init{'$name'}) ne 'HASH';\n";
	169	$out .= " \$r->$elem = '${type}'->new($init);$cmt\n";
8cc95fdb	170	$classes{$name} = $type;
	171	$got_class = 1;
	172	}
	173	else{
	174	croak "'$type' is not a valid struct element type";
	175	}
	176	$idx += 2;
	177	}
430530ea	178	$out .= " bless \$r, \$class;\n }\n";
8cc95fdb	179
	180	# Create accessor methods.
	181
8cc95fdb	182	my( $pre, $pst, $sel );
	183	$cnt = 0;
	184	foreach $name (@methods){
	185	if ( do { no strict 'refs'; defined &{$class . "::$name"} } ) {
22d4bb9c	186	warnings::warnif("function '$name' already defined, overrides struct accessor method");
8cc95fdb	187	}
	188	else {
	189	$pre = $pst = $cmt = $sel = '';
	190	if( defined $refs{$name} ){
	191	$pre = "\\(";
	192	$pst = ")";
	193	$cmt = " # returns ref";
	194	}
	195	$out .= " sub $name {$cmt\n my \$r = shift;\n";
	196	if( $base_type eq 'ARRAY' ){
	197	$elem = "[$cnt]";
	198	++$cnt;
	199	}
	200	elsif( $base_type eq 'HASH' ){
430530ea	201	$elem = "{'${class}::$name'}";
8cc95fdb	202	}
	203	if( defined $arrays{$name} ){
	204	$out .= " my \$i;\n";
430530ea	205	$out .= " \@_ ? (\$i = shift) : return \$r->$elem;\n";
8cc95fdb	206	$sel = "->[\$i]";
	207	}
	208	elsif( defined $hashes{$name} ){
	209	$out .= " my \$i;\n";
430530ea	210	$out .= " \@_ ? (\$i = shift) : return \$r->$elem;\n";
8cc95fdb	211	$sel = "->{\$i}";
	212	}
	213	elsif( defined $classes{$name} ){
	214	if ( $CHECK_CLASS_MEMBERSHIP ) {
20408e3c	215	$out .= " croak '$name argument is wrong class' if \@_ && ! UNIVERSAL::isa(\$_[0], '$classes{$name}');\n";
8cc95fdb	216	}
	217	}
	218	$out .= " croak 'Too many args to $name' if \@_ > 1;\n";
	219	$out .= " \@_ ? ($pre\$r->$elem$sel = shift$pst) : $pre\$r->$elem$sel$pst;\n";
	220	$out .= " }\n";
	221	}
	222	}
	223	$out .= "}\n1;\n";
	224
	225	print $out if $print;
	226	my $result = eval $out;
	227	carp $@ if $@;
	228	}
	229
	230	sub _usage_error {
	231	confess "struct usage error";
	232	}
	233
	234	sub _subclass_error {
	235	croak 'struct class cannot be a subclass (@ISA not allowed)';
	236	}
	237
	238	1; # for require
	239
	240
	241	__END__
	242
	243	=head1 NAME
	244
	245	Class::Struct - declare struct-like datatypes as Perl classes
	246
	247	=head1 SYNOPSIS
	248
	249	use Class::Struct;
	250	# declare struct, based on array:
	251	struct( CLASS_NAME => [ ELEMENT_NAME => ELEMENT_TYPE, ... ]);
	252	# declare struct, based on hash:
	253	struct( CLASS_NAME => { ELEMENT_NAME => ELEMENT_TYPE, ... });
	254
	255	package CLASS_NAME;
	256	use Class::Struct;
	257	# declare struct, based on array, implicit class name:
	258	struct( ELEMENT_NAME => ELEMENT_TYPE, ... );
	259
0e06870b	260	# Declare struct at compile time
	261	use Class::Struct CLASS_NAME => [ ELEMENT_NAME => ELEMENT_TYPE, ... ];
	262	use Class::Struct CLASS_NAME => { ELEMENT_NAME => ELEMENT_TYPE, ... };
8cc95fdb	263
	264	package Myobj;
	265	use Class::Struct;
	266	# declare struct with four types of elements:
	267	struct( s => '$', a => '@', h => '%', c => 'My_Other_Class' );
	268
	269	$obj = new Myobj; # constructor
	270
	271	# scalar type accessor:
	272	$element_value = $obj->s; # element value
	273	$obj->s('new value'); # assign to element
	274
	275	# array type accessor:
	276	$ary_ref = $obj->a; # reference to whole array
	277	$ary_element_value = $obj->a(2); # array element value
	278	$obj->a(2, 'new value'); # assign to array element
	279
	280	# hash type accessor:
	281	$hash_ref = $obj->h; # reference to whole hash
	282	$hash_element_value = $obj->h('x'); # hash element value
0e06870b	283	$obj->h('x', 'new value'); # assign to hash element
8cc95fdb	284
	285	# class type accessor:
	286	$element_value = $obj->c; # object reference
	287	$obj->c->method(...); # call method of object
	288	$obj->c(new My_Other_Class); # assign a new object
	289
8cc95fdb	290	=head1 DESCRIPTION
	291
	292	C<Class::Struct> exports a single function, C<struct>.
	293	Given a list of element names and types, and optionally
	294	a class name, C<struct> creates a Perl 5 class that implements
	295	a "struct-like" data structure.
	296
	297	The new class is given a constructor method, C<new>, for creating
	298	struct objects.
	299
	300	Each element in the struct data has an accessor method, which is
	301	used to assign to the element and to fetch its value. The
	302	default accessor can be overridden by declaring a C<sub> of the
	303	same name in the package. (See Example 2.)
	304
	305	Each element's type can be scalar, array, hash, or class.
	306
8cc95fdb	307	=head2 The C<struct()> function
	308
	309	The C<struct> function has three forms of parameter-list.
	310
	311	struct( CLASS_NAME => [ ELEMENT_LIST ]);
	312	struct( CLASS_NAME => { ELEMENT_LIST });
	313	struct( ELEMENT_LIST );
	314
	315	The first and second forms explicitly identify the name of the
	316	class being created. The third form assumes the current package
	317	name as the class name.
	318
	319	An object of a class created by the first and third forms is
	320	based on an array, whereas an object of a class created by the
	321	second form is based on a hash. The array-based forms will be
	322	somewhat faster and smaller; the hash-based forms are more
	323	flexible.
	324
	325	The class created by C<struct> must not be a subclass of another
	326	class other than C<UNIVERSAL>.
	327
430530ea	328	It can, however, be used as a superclass for other classes. To facilitate
	329	this, the generated constructor method uses a two-argument blessing.
	330	Furthermore, if the class is hash-based, the key of each element is
	331	prefixed with the class name (see I<Perl Cookbook>, Recipe 13.12).
	332
8cc95fdb	333	A function named C<new> must not be explicitly defined in a class
	334	created by C<struct>.
	335
	336	The I<ELEMENT_LIST> has the form
	337
	338	NAME => TYPE, ...
	339
	340	Each name-type pair declares one element of the struct. Each
	341	element name will be defined as an accessor method unless a
	342	method by that name is explicitly defined; in the latter case, a
103ff8e3	343	warning is issued if the warning flag (B<-w>) is set.
8cc95fdb	344
0e06870b	345	=head2 Class Creation at Compile Time
	346
	347	C<Class::Struct> can create your class at compile time. The main reason
	348	for doing this is obvious, so your class acts like every other class in
	349	Perl. Creating your class at compile time will make the order of events
	350	similar to using any other class ( or Perl module ).
	351
	352	There is no significant speed gain between compile time and run time
	353	class creation, there is just a new, more standard order of events.
8cc95fdb	354
	355	=head2 Element Types and Accessor Methods
	356
	357	The four element types -- scalar, array, hash, and class -- are
	358	represented by strings -- C<'$'>, C<'@'>, C<'%'>, and a class name --
	359	optionally preceded by a C<'*'>.
	360
	361	The accessor method provided by C<struct> for an element depends
	362	on the declared type of the element.
	363
	364	=over
	365
	366	=item Scalar (C<'$'> or C<'*$'>)
	367
430530ea	368	The element is a scalar, and by default is initialized to C<undef>
430530ea	369	(but see L<Initializing with new>).
8cc95fdb	370
	371	The accessor's argument, if any, is assigned to the element.
	372
	373	If the element type is C<'$'>, the value of the element (after
	374	assignment) is returned. If the element type is C<'*$'>, a reference
	375	to the element is returned.
	376
	377	=item Array (C<'@'> or C<'*@'>)
	378
430530ea	379	The element is an array, initialized by default to C<()>.
8cc95fdb	380
8cc95fdb	381	With no argument, the accessor returns a reference to the
430530ea	382	element's whole array (whether or not the element was
cb50131a	383	specified as C<'@'> or C<'*@'>).
8cc95fdb	384
	385	With one or two arguments, the first argument is an index
	386	specifying one element of the array; the second argument, if
	387	present, is assigned to the array element. If the element type
	388	is C<'@'>, the accessor returns the array element value. If the
	389	element type is C<'*@'>, a reference to the array element is
	390	returned.
	391
	392	=item Hash (C<'%'> or C<'*%'>)
	393
430530ea	394	The element is a hash, initialized by default to C<()>.
8cc95fdb	395
8cc95fdb	396	With no argument, the accessor returns a reference to the
430530ea	397	element's whole hash (whether or not the element was
cb50131a	398	specified as C<'%'> or C<'*%'>).
8cc95fdb	399
	400	With one or two arguments, the first argument is a key specifying
	401	one element of the hash; the second argument, if present, is
	402	assigned to the hash element. If the element type is C<'%'>, the
	403	accessor returns the hash element value. If the element type is
	404	C<'*%'>, a reference to the hash element is returned.
	405
	406	=item Class (C<'Class_Name'> or C<'*Class_Name'>)
	407
	408	The element's value must be a reference blessed to the named
	409	class or to one of its subclasses. The element is initialized to
	410	the result of calling the C<new> constructor of the named class.
	411
	412	The accessor's argument, if any, is assigned to the element. The
	413	accessor will C<croak> if this is not an appropriate object
	414	reference.
	415
	416	If the element type does not start with a C<'*'>, the accessor
	417	returns the element value (after assignment). If the element type
	418	starts with a C<'*'>, a reference to the element itself is returned.
	419
	420	=back
	421
430530ea	422	=head2 Initializing with C<new>
	423
	424	C<struct> always creates a constructor called C<new>. That constructor
	425	may take a list of initializers for the various elements of the new
	426	struct.
	427
	428	Each initializer is a pair of values: I<element name>C< =E<gt> >I<value>.
	429	The initializer value for a scalar element is just a scalar value. The
	430	initializer for an array element is an array reference. The initializer
	431	for a hash is a hash reference.
	432
	433	The initializer for a class element is also a hash reference, and the
	434	contents of that hash are passed to the element's own constructor.
	435
	436	See Example 3 below for an example of initialization.
	437
8cc95fdb	438	=head1 EXAMPLES
	439
	440	=over
	441
	442	=item Example 1
	443
	444	Giving a struct element a class type that is also a struct is how
	445	structs are nested. Here, C<timeval> represents a time (seconds and
	446	microseconds), and C<rusage> has two elements, each of which is of
	447	type C<timeval>.
	448
	449	use Class::Struct;
	450
	451	struct( rusage => {
	452	ru_utime => timeval, # seconds
	453	ru_stime => timeval, # microseconds
	454	});
	455
	456	struct( timeval => [
	457	tv_secs => '$',
	458	tv_usecs => '$',
	459	]);
	460
	461	# create an object:
	462	my $t = new rusage;
8cc95fdb	463
430530ea	464	# $t->ru_utime and $t->ru_stime are objects of type timeval.
8cc95fdb	465	# set $t->ru_utime to 100.0 sec and $t->ru_stime to 5.0 sec.
	466	$t->ru_utime->tv_secs(100);
	467	$t->ru_utime->tv_usecs(0);
	468	$t->ru_stime->tv_secs(5);
	469	$t->ru_stime->tv_usecs(0);
	470
8cc95fdb	471	=item Example 2
	472
	473	An accessor function can be redefined in order to provide
	474	additional checking of values, etc. Here, we want the C<count>
	475	element always to be nonnegative, so we redefine the C<count>
	476	accessor accordingly.
	477
	478	package MyObj;
	479	use Class::Struct;
	480
430530ea	481	# declare the struct
8cc95fdb	482	struct ( 'MyObj', { count => '$', stuff => '%' } );
8cc95fdb	483
430530ea	484	# override the default accessor method for 'count'
8cc95fdb	485	sub count {
	486	my $self = shift;
	487	if ( @_ ) {
	488	die 'count must be nonnegative' if $_[0] < 0;
	489	$self->{'count'} = shift;
	490	warn "Too many args to count" if @_;
	491	}
	492	return $self->{'count'};
	493	}
	494
	495	package main;
	496	$x = new MyObj;
	497	print "\$x->count(5) = ", $x->count(5), "\n";
	498	# prints '$x->count(5) = 5'
	499
	500	print "\$x->count = ", $x->count, "\n";
	501	# prints '$x->count = 5'
	502
	503	print "\$x->count(-5) = ", $x->count(-5), "\n";
	504	# dies due to negative argument!
	505
430530ea	506	=item Example 3
	507
	508	The constructor of a generated class can be passed a list
	509	of I<element>=>I<value> pairs, with which to initialize the struct.
	510	If no initializer is specified for a particular element, its default
	511	initialization is performed instead. Initializers for non-existent
	512	elements are silently ignored.
	513
	514	Note that the initializer for a nested struct is specified
	515	as an anonymous hash of initializers, which is passed on to the nested
	516	struct's constructor.
	517
430530ea	518	use Class::Struct;
	519
	520	struct Breed =>
	521	{
	522	name => '$',
	523	cross => '$',
	524	};
	525
	526	struct Cat =>
	527	[
	528	name => '$',
	529	kittens => '@',
	530	markings => '%',
	531	breed => 'Breed',
	532	];
	533
	534
	535	my $cat = Cat->new( name => 'Socks',
	536	kittens => ['Monica', 'Kenneth'],
	537	markings => { socks=>1, blaze=>"white" },
	538	breed => { name=>'short-hair', cross=>1 },
	539	);
	540
	541	print "Once a cat called ", $cat->name, "\n";
	542	print "(which was a ", $cat->breed->name, ")\n";
	543	print "had two kittens: ", join(' and ', @{$cat->kittens}), "\n";
	544
cb50131a	545	=back
8cc95fdb	546
	547	=head1 Author and Modification History
	548
0e06870b	549	Modified by Casey Tweten, 2000-11-08, v0.59.
	550
	551	Added the ability for compile time class creation.
8cc95fdb	552
430530ea	553	Modified by Damian Conway, 1999-03-05, v0.58.
	554
	555	Added handling of hash-like arg list to class ctor.
	556
	557	Changed to two-argument blessing in ctor to support
	558	derivation from created classes.
	559
	560	Added classname prefixes to keys in hash-based classes
	561	(refer to "Perl Cookbook", Recipe 13.12 for rationale).
	562
	563	Corrected behaviour of accessors for '@' and '%' struct
	564	elements. Package now implements documented behaviour when
	565	returning a reference to an entire hash or array element.
	566	Previously these were returned as a reference to a reference
	567	to the element.
	568
8cc95fdb	569	Renamed to C<Class::Struct> and modified by Jim Miner, 1997-04-02.
	570
	571	members() function removed.
	572	Documentation corrected and extended.
	573	Use of struct() in a subclass prohibited.
	574	User definition of accessor allowed.
	575	Treatment of '*' in element types corrected.
	576	Treatment of classes as element types corrected.
	577	Class name to struct() made optional.
	578	Diagnostic checks added.
	579
8cc95fdb	580	Originally C<Class::Template> by Dean Roehrich.
	581
	582	# Template.pm --- struct/member template builder
	583	# 12mar95
	584	# Dean Roehrich
	585	#
	586	# changes/bugs fixed since 28nov94 version:
	587	# - podified
	588	# changes/bugs fixed since 21nov94 version:
	589	# - Fixed examples.
	590	# changes/bugs fixed since 02sep94 version:
	591	# - Moved to Class::Template.
	592	# changes/bugs fixed since 20feb94 version:
	593	# - Updated to be a more proper module.
	594	# - Added "use strict".
	595	# - Bug in build_methods, was using @var when @$var needed.
	596	# - Now using my() rather than local().
	597	#
	598	# Uses perl5 classes to create nested data types.
	599	# This is offered as one implementation of Tom Christiansen's "structs.pl"
	600	# idea.
	601
	602	=cut