[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 = '0.58';

## 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 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 . "::$name"} } ) {
            warnings::warn "function '$name' already defined, overrides struct accessor method"
                if warnings::enabled();
        }
        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, ... );


    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 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 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
17f410f9	5	use 5.005_64;
8cc95fdb	6
8cc95fdb	7	use strict;
d3a7d8c7	8	use warnings::register;
17f410f9	9	our(@ISA, @EXPORT, $VERSION);
8cc95fdb	10
	11	use Carp;
	12
	13	require Exporter;
	14	@ISA = qw(Exporter);
	15	@EXPORT = qw(struct);
	16
430530ea	17	$VERSION = '0.58';
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
	54	sub struct {
	55
	56	# Determine parameter list structure, one of:
	57	# struct( class => [ element-list ])
	58	# struct( class => { element-list })
	59	# struct( element-list )
	60	# Latter form assumes current package name as struct name.
	61
	62	my ($class, @decls);
	63	my $base_type = ref $_[1];
	64	if ( $base_type eq 'HASH' ) {
	65	$class = shift;
	66	@decls = %{shift()};
	67	_usage_error() if @_;
	68	}
	69	elsif ( $base_type eq 'ARRAY' ) {
	70	$class = shift;
	71	@decls = @{shift()};
	72	_usage_error() if @_;
	73	}
	74	else {
	75	$base_type = 'ARRAY';
	76	$class = (caller())[0];
	77	@decls = @_;
	78	}
	79	_usage_error() if @decls % 2 == 1;
	80
	81	# Ensure we are not, and will not be, a subclass.
	82
	83	my $isa = do {
	84	no strict 'refs';
	85	\@{$class . '::ISA'};
	86	};
	87	_subclass_error() if @$isa;
	88	tie @$isa, 'Class::Struct::Tie_ISA';
	89
	90	# Create constructor.
	91
	92	croak "function 'new' already defined in package $class"
	93	if do { no strict 'refs'; defined &{$class . "::new"} };
	94
	95	my @methods = ();
	96	my %refs = ();
	97	my %arrays = ();
	98	my %hashes = ();
	99	my %classes = ();
	100	my $got_class = 0;
	101	my $out = '';
	102
	103	$out = "{\n package $class;\n use Carp;\n sub new {\n";
430530ea	104	$out .= " my (\$class, \%init) = \@_;\n";
f01e5ef6	105	$out .= " \$class = __PACKAGE__ unless \@_;\n";
8cc95fdb	106
	107	my $cnt = 0;
	108	my $idx = 0;
	109	my( $cmt, $name, $type, $elem );
	110
	111	if( $base_type eq 'HASH' ){
	112	$out .= " my(\$r) = {};\n";
	113	$cmt = '';
	114	}
	115	elsif( $base_type eq 'ARRAY' ){
	116	$out .= " my(\$r) = [];\n";
	117	}
	118	while( $idx < @decls ){
	119	$name = $decls[$idx];
	120	$type = $decls[$idx+1];
	121	push( @methods, $name );
	122	if( $base_type eq 'HASH' ){
430530ea	123	$elem = "{'${class}::$name'}";
8cc95fdb	124	}
	125	elsif( $base_type eq 'ARRAY' ){
	126	$elem = "[$cnt]";
	127	++$cnt;
	128	$cmt = " # $name";
	129	}
	130	if( $type =~ /^\*(.)/ ){
	131	$refs{$name}++;
	132	$type = $1;
	133	}
430530ea	134	my $init = "defined(\$init{'$name'}) ? \$init{'$name'} :";
8cc95fdb	135	if( $type eq '@' ){
430530ea	136	$out .= " croak 'Initializer for $name must be array reference'\n";
	137	$out .= " if defined(\$init{'$name'}) && ref(\$init{'$name'}) ne 'ARRAY';\n";
	138	$out .= " \$r->$elem = $init [];$cmt\n";
8cc95fdb	139	$arrays{$name}++;
	140	}
	141	elsif( $type eq '%' ){
430530ea	142	$out .= " croak 'Initializer for $name must be hash reference'\n";
	143	$out .= " if defined(\$init{'$name'}) && ref(\$init{'$name'}) ne 'HASH';\n";
	144	$out .= " \$r->$elem = $init {};$cmt\n";
8cc95fdb	145	$hashes{$name}++;
	146	}
	147	elsif ( $type eq '$') {
430530ea	148	$out .= " \$r->$elem = $init undef;$cmt\n";
8cc95fdb	149	}
8cc95fdb	150	elsif( $type =~ /^\w+(?:::\w+)*$/ ){
430530ea	151	$init = "defined(\$init{'$name'}) ? \%{\$init{'$name'}} : ()";
	152	$out .= " croak 'Initializer for $name must be hash reference'\n";
	153	$out .= " if defined(\$init{'$name'}) && ref(\$init{'$name'}) ne 'HASH';\n";
	154	$out .= " \$r->$elem = '${type}'->new($init);$cmt\n";
8cc95fdb	155	$classes{$name} = $type;
	156	$got_class = 1;
	157	}
	158	else{
	159	croak "'$type' is not a valid struct element type";
	160	}
	161	$idx += 2;
	162	}
430530ea	163	$out .= " bless \$r, \$class;\n }\n";
8cc95fdb	164
	165	# Create accessor methods.
	166
8cc95fdb	167	my( $pre, $pst, $sel );
	168	$cnt = 0;
	169	foreach $name (@methods){
	170	if ( do { no strict 'refs'; defined &{$class . "::$name"} } ) {
d3a7d8c7	171	warnings::warn "function '$name' already defined, overrides struct accessor method"
d3a7d8c7	172	if warnings::enabled();
8cc95fdb	173	}
	174	else {
	175	$pre = $pst = $cmt = $sel = '';
	176	if( defined $refs{$name} ){
	177	$pre = "\\(";
	178	$pst = ")";
	179	$cmt = " # returns ref";
	180	}
	181	$out .= " sub $name {$cmt\n my \$r = shift;\n";
	182	if( $base_type eq 'ARRAY' ){
	183	$elem = "[$cnt]";
	184	++$cnt;
	185	}
	186	elsif( $base_type eq 'HASH' ){
430530ea	187	$elem = "{'${class}::$name'}";
8cc95fdb	188	}
	189	if( defined $arrays{$name} ){
	190	$out .= " my \$i;\n";
430530ea	191	$out .= " \@_ ? (\$i = shift) : return \$r->$elem;\n";
8cc95fdb	192	$sel = "->[\$i]";
	193	}
	194	elsif( defined $hashes{$name} ){
	195	$out .= " my \$i;\n";
430530ea	196	$out .= " \@_ ? (\$i = shift) : return \$r->$elem;\n";
8cc95fdb	197	$sel = "->{\$i}";
	198	}
	199	elsif( defined $classes{$name} ){
	200	if ( $CHECK_CLASS_MEMBERSHIP ) {
20408e3c	201	$out .= " croak '$name argument is wrong class' if \@_ && ! UNIVERSAL::isa(\$_[0], '$classes{$name}');\n";
8cc95fdb	202	}
	203	}
	204	$out .= " croak 'Too many args to $name' if \@_ > 1;\n";
	205	$out .= " \@_ ? ($pre\$r->$elem$sel = shift$pst) : $pre\$r->$elem$sel$pst;\n";
	206	$out .= " }\n";
	207	}
	208	}
	209	$out .= "}\n1;\n";
	210
	211	print $out if $print;
	212	my $result = eval $out;
	213	carp $@ if $@;
	214	}
	215
	216	sub _usage_error {
	217	confess "struct usage error";
	218	}
	219
	220	sub _subclass_error {
	221	croak 'struct class cannot be a subclass (@ISA not allowed)';
	222	}
	223
	224	1; # for require
	225
	226
	227	__END__
	228
	229	=head1 NAME
	230
	231	Class::Struct - declare struct-like datatypes as Perl classes
	232
	233	=head1 SYNOPSIS
	234
	235	use Class::Struct;
	236	# declare struct, based on array:
	237	struct( CLASS_NAME => [ ELEMENT_NAME => ELEMENT_TYPE, ... ]);
	238	# declare struct, based on hash:
	239	struct( CLASS_NAME => { ELEMENT_NAME => ELEMENT_TYPE, ... });
	240
	241	package CLASS_NAME;
	242	use Class::Struct;
	243	# declare struct, based on array, implicit class name:
	244	struct( ELEMENT_NAME => ELEMENT_TYPE, ... );
	245
	246
	247	package Myobj;
	248	use Class::Struct;
	249	# declare struct with four types of elements:
	250	struct( s => '$', a => '@', h => '%', c => 'My_Other_Class' );
	251
	252	$obj = new Myobj; # constructor
	253
	254	# scalar type accessor:
	255	$element_value = $obj->s; # element value
	256	$obj->s('new value'); # assign to element
	257
	258	# array type accessor:
	259	$ary_ref = $obj->a; # reference to whole array
	260	$ary_element_value = $obj->a(2); # array element value
	261	$obj->a(2, 'new value'); # assign to array element
	262
	263	# hash type accessor:
	264	$hash_ref = $obj->h; # reference to whole hash
	265	$hash_element_value = $obj->h('x'); # hash element value
266	$obj->h('x', 'new value'); # assign to hash element
267
268	# class type accessor:
269	$element_value = $obj->c; # object reference
270	$obj->c->method(...); # call method of object
271	$obj->c(new My_Other_Class); # assign a new object
272
273
274	=head1 DESCRIPTION
275
276	C<Class::Struct> exports a single function, C<struct>.
277	Given a list of element names and types, and optionally
278	a class name, C<struct> creates a Perl 5 class that implements
279	a "struct-like" data structure.
280
281	The new class is given a constructor method, C<new>, for creating
282	struct objects.
283
284	Each element in the struct data has an accessor method, which is
285	used to assign to the element and to fetch its value. The
286	default accessor can be overridden by declaring a C<sub> of the
287	same name in the package. (See Example 2.)
288
289	Each element's type can be scalar, array, hash, or class.
290
291
292	=head2 The C<struct()> function
293
294	The C<struct> function has three forms of parameter-list.
295
296	struct( CLASS_NAME => [ ELEMENT_LIST ]);
297	struct( CLASS_NAME => { ELEMENT_LIST });
298	struct( ELEMENT_LIST );
299
300	The first and second forms explicitly identify the name of the
301	class being created. The third form assumes the current package
302	name as the class name.
303
304	An object of a class created by the first and third forms is
305	based on an array, whereas an object of a class created by the
306	second form is based on a hash. The array-based forms will be
307	somewhat faster and smaller; the hash-based forms are more
308	flexible.
309
310	The class created by C<struct> must not be a subclass of another
311	class other than C<UNIVERSAL>.
312
430530ea	313	It can, however, be used as a superclass for other classes. To facilitate
	314	this, the generated constructor method uses a two-argument blessing.
	315	Furthermore, if the class is hash-based, the key of each element is
	316	prefixed with the class name (see I<Perl Cookbook>, Recipe 13.12).
	317
8cc95fdb	318	A function named C<new> must not be explicitly defined in a class
	319	created by C<struct>.
	320
	321	The I<ELEMENT_LIST> has the form
	322
	323	NAME => TYPE, ...
	324
	325	Each name-type pair declares one element of the struct. Each
	326	element name will be defined as an accessor method unless a
	327	method by that name is explicitly defined; in the latter case, a
103ff8e3	328	warning is issued if the warning flag (B<-w>) is set.
8cc95fdb	329
	330
	331	=head2 Element Types and Accessor Methods
	332
	333	The four element types -- scalar, array, hash, and class -- are
	334	represented by strings -- C<'$'>, C<'@'>, C<'%'>, and a class name --
	335	optionally preceded by a C<'*'>.
	336
	337	The accessor method provided by C<struct> for an element depends
	338	on the declared type of the element.
	339
	340	=over
	341
	342	=item Scalar (C<'$'> or C<'*$'>)
	343
430530ea	344	The element is a scalar, and by default is initialized to C<undef>
430530ea	345	(but see L<Initializing with new>).
8cc95fdb	346
	347	The accessor's argument, if any, is assigned to the element.
	348
	349	If the element type is C<'$'>, the value of the element (after
	350	assignment) is returned. If the element type is C<'*$'>, a reference
	351	to the element is returned.
	352
	353	=item Array (C<'@'> or C<'*@'>)
	354
430530ea	355	The element is an array, initialized by default to C<()>.
8cc95fdb	356
8cc95fdb	357	With no argument, the accessor returns a reference to the
430530ea	358	element's whole array (whether or not the element was
58231d39	359	specified as C<'@'> or C<'*@'>).
8cc95fdb	360
	361	With one or two arguments, the first argument is an index
	362	specifying one element of the array; the second argument, if
	363	present, is assigned to the array element. If the element type
	364	is C<'@'>, the accessor returns the array element value. If the
	365	element type is C<'*@'>, a reference to the array element is
	366	returned.
	367
	368	=item Hash (C<'%'> or C<'*%'>)
	369
430530ea	370	The element is a hash, initialized by default to C<()>.
8cc95fdb	371
8cc95fdb	372	With no argument, the accessor returns a reference to the
430530ea	373	element's whole hash (whether or not the element was
58231d39	374	specified as C<'%'> or C<'*%'>).
8cc95fdb	375
	376	With one or two arguments, the first argument is a key specifying
	377	one element of the hash; the second argument, if present, is
	378	assigned to the hash element. If the element type is C<'%'>, the
	379	accessor returns the hash element value. If the element type is
	380	C<'*%'>, a reference to the hash element is returned.
	381
	382	=item Class (C<'Class_Name'> or C<'*Class_Name'>)
	383
	384	The element's value must be a reference blessed to the named
	385	class or to one of its subclasses. The element is initialized to
	386	the result of calling the C<new> constructor of the named class.
	387
	388	The accessor's argument, if any, is assigned to the element. The
	389	accessor will C<croak> if this is not an appropriate object
	390	reference.
	391
	392	If the element type does not start with a C<'*'>, the accessor
	393	returns the element value (after assignment). If the element type
	394	starts with a C<'*'>, a reference to the element itself is returned.
	395
	396	=back
	397
430530ea	398	=head2 Initializing with C<new>
	399
	400	C<struct> always creates a constructor called C<new>. That constructor
	401	may take a list of initializers for the various elements of the new
	402	struct.
	403
	404	Each initializer is a pair of values: I<element name>C< =E<gt> >I<value>.
	405	The initializer value for a scalar element is just a scalar value. The
	406	initializer for an array element is an array reference. The initializer
	407	for a hash is a hash reference.
	408
	409	The initializer for a class element is also a hash reference, and the
	410	contents of that hash are passed to the element's own constructor.
	411
	412	See Example 3 below for an example of initialization.
	413
	414
8cc95fdb	415	=head1 EXAMPLES
	416
	417	=over
	418
	419	=item Example 1
	420
	421	Giving a struct element a class type that is also a struct is how
	422	structs are nested. Here, C<timeval> represents a time (seconds and
	423	microseconds), and C<rusage> has two elements, each of which is of
	424	type C<timeval>.
	425
	426	use Class::Struct;
	427
	428	struct( rusage => {
	429	ru_utime => timeval, # seconds
	430	ru_stime => timeval, # microseconds
	431	});
	432
	433	struct( timeval => [
	434	tv_secs => '$',
	435	tv_usecs => '$',
	436	]);
	437
	438	# create an object:
	439	my $t = new rusage;
8cc95fdb	440
430530ea	441	# $t->ru_utime and $t->ru_stime are objects of type timeval.
8cc95fdb	442	# set $t->ru_utime to 100.0 sec and $t->ru_stime to 5.0 sec.
	443	$t->ru_utime->tv_secs(100);
	444	$t->ru_utime->tv_usecs(0);
	445	$t->ru_stime->tv_secs(5);
	446	$t->ru_stime->tv_usecs(0);
	447
	448
	449	=item Example 2
	450
	451	An accessor function can be redefined in order to provide
	452	additional checking of values, etc. Here, we want the C<count>
	453	element always to be nonnegative, so we redefine the C<count>
	454	accessor accordingly.
	455
	456	package MyObj;
	457	use Class::Struct;
	458
430530ea	459	# declare the struct
8cc95fdb	460	struct ( 'MyObj', { count => '$', stuff => '%' } );
8cc95fdb	461
430530ea	462	# override the default accessor method for 'count'
8cc95fdb	463	sub count {
	464	my $self = shift;
	465	if ( @_ ) {
	466	die 'count must be nonnegative' if $_[0] < 0;
	467	$self->{'count'} = shift;
	468	warn "Too many args to count" if @_;
	469	}
	470	return $self->{'count'};
	471	}
	472
	473	package main;
	474	$x = new MyObj;
	475	print "\$x->count(5) = ", $x->count(5), "\n";
	476	# prints '$x->count(5) = 5'
	477
	478	print "\$x->count = ", $x->count, "\n";
	479	# prints '$x->count = 5'
	480
	481	print "\$x->count(-5) = ", $x->count(-5), "\n";
	482	# dies due to negative argument!
	483
430530ea	484	=item Example 3
	485
	486	The constructor of a generated class can be passed a list
	487	of I<element>=>I<value> pairs, with which to initialize the struct.
	488	If no initializer is specified for a particular element, its default
	489	initialization is performed instead. Initializers for non-existent
	490	elements are silently ignored.
	491
	492	Note that the initializer for a nested struct is specified
	493	as an anonymous hash of initializers, which is passed on to the nested
	494	struct's constructor.
	495
	496
	497	use Class::Struct;
	498
	499	struct Breed =>
	500	{
	501	name => '$',
	502	cross => '$',
	503	};
	504
	505	struct Cat =>
	506	[
	507	name => '$',
	508	kittens => '@',
	509	markings => '%',
	510	breed => 'Breed',
	511	];
	512
	513
	514	my $cat = Cat->new( name => 'Socks',
	515	kittens => ['Monica', 'Kenneth'],
	516	markings => { socks=>1, blaze=>"white" },
	517	breed => { name=>'short-hair', cross=>1 },
	518	);
	519
	520	print "Once a cat called ", $cat->name, "\n";
	521	print "(which was a ", $cat->breed->name, ")\n";
	522	print "had two kittens: ", join(' and ', @{$cat->kittens}), "\n";
	523
a45bd81d	524	=back
8cc95fdb	525
	526	=head1 Author and Modification History
	527
	528
430530ea	529	Modified by Damian Conway, 1999-03-05, v0.58.
	530
	531	Added handling of hash-like arg list to class ctor.
	532
	533	Changed to two-argument blessing in ctor to support
	534	derivation from created classes.
	535
	536	Added classname prefixes to keys in hash-based classes
	537	(refer to "Perl Cookbook", Recipe 13.12 for rationale).
	538
	539	Corrected behaviour of accessors for '@' and '%' struct
	540	elements. Package now implements documented behaviour when
	541	returning a reference to an entire hash or array element.
	542	Previously these were returned as a reference to a reference
	543	to the element.
	544
	545
8cc95fdb	546	Renamed to C<Class::Struct> and modified by Jim Miner, 1997-04-02.
	547
	548	members() function removed.
	549	Documentation corrected and extended.
	550	Use of struct() in a subclass prohibited.
	551	User definition of accessor allowed.
	552	Treatment of '*' in element types corrected.
	553	Treatment of classes as element types corrected.
	554	Class name to struct() made optional.
	555	Diagnostic checks added.
	556
	557
	558	Originally C<Class::Template> by Dean Roehrich.
	559
	560	# Template.pm --- struct/member template builder
	561	# 12mar95
	562	# Dean Roehrich
	563	#
	564	# changes/bugs fixed since 28nov94 version:
	565	# - podified
	566	# changes/bugs fixed since 21nov94 version:
	567	# - Fixed examples.
	568	# changes/bugs fixed since 02sep94 version:
	569	# - Moved to Class::Template.
	570	# changes/bugs fixed since 20feb94 version:
	571	# - Updated to be a more proper module.
	572	# - Added "use strict".
	573	# - Bug in build_methods, was using @var when @$var needed.
	574	# - Now using my() rather than local().
	575	#
	576	# Uses perl5 classes to create nested data types.
	577	# This is offered as one implementation of Tom Christiansen's "structs.pl"
	578	# idea.
	579
	580	=cut