[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 ( @_ % 2 == 0 ) {
      &struct;
    } else {
      $self->export_to_level( 1, $self, @EXPORT );
    }
}

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
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
ab6e6725	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
ab6e6725	54	sub import {
	55	my $self = shift;
	56
ad6edfcb	57	if ( @_ % 2 == 0 ) {
ab6e6725	58	&struct;
	59	} else {
	60	$self->export_to_level( 1, $self, @EXPORT );
	61	}
	62	}
	63
8cc95fdb	64	sub struct {
	65
	66	# Determine parameter list structure, one of:
	67	# struct( class => [ element-list ])
	68	# struct( class => { element-list })
	69	# struct( element-list )
	70	# Latter form assumes current package name as struct name.
	71
	72	my ($class, @decls);
	73	my $base_type = ref $_[1];
	74	if ( $base_type eq 'HASH' ) {
	75	$class = shift;
	76	@decls = %{shift()};
	77	_usage_error() if @_;
	78	}
	79	elsif ( $base_type eq 'ARRAY' ) {
	80	$class = shift;
	81	@decls = @{shift()};
	82	_usage_error() if @_;
	83	}
	84	else {
	85	$base_type = 'ARRAY';
	86	$class = (caller())[0];
	87	@decls = @_;
	88	}
ad6edfcb	89
8cc95fdb	90	_usage_error() if @decls % 2 == 1;
	91
	92	# Ensure we are not, and will not be, a subclass.
	93
	94	my $isa = do {
	95	no strict 'refs';
	96	\@{$class . '::ISA'};
	97	};
	98	_subclass_error() if @$isa;
	99	tie @$isa, 'Class::Struct::Tie_ISA';
	100
	101	# Create constructor.
	102
	103	croak "function 'new' already defined in package $class"
	104	if do { no strict 'refs'; defined &{$class . "::new"} };
	105
	106	my @methods = ();
	107	my %refs = ();
	108	my %arrays = ();
	109	my %hashes = ();
	110	my %classes = ();
	111	my $got_class = 0;
	112	my $out = '';
	113
	114	$out = "{\n package $class;\n use Carp;\n sub new {\n";
430530ea	115	$out .= " my (\$class, \%init) = \@_;\n";
f01e5ef6	116	$out .= " \$class = __PACKAGE__ unless \@_;\n";
8cc95fdb	117
	118	my $cnt = 0;
	119	my $idx = 0;
	120	my( $cmt, $name, $type, $elem );
	121
	122	if( $base_type eq 'HASH' ){
	123	$out .= " my(\$r) = {};\n";
	124	$cmt = '';
	125	}
	126	elsif( $base_type eq 'ARRAY' ){
	127	$out .= " my(\$r) = [];\n";
	128	}
	129	while( $idx < @decls ){
	130	$name = $decls[$idx];
	131	$type = $decls[$idx+1];
	132	push( @methods, $name );
	133	if( $base_type eq 'HASH' ){
430530ea	134	$elem = "{'${class}::$name'}";
8cc95fdb	135	}
	136	elsif( $base_type eq 'ARRAY' ){
	137	$elem = "[$cnt]";
	138	++$cnt;
	139	$cmt = " # $name";
	140	}
	141	if( $type =~ /^\*(.)/ ){
	142	$refs{$name}++;
	143	$type = $1;
	144	}
430530ea	145	my $init = "defined(\$init{'$name'}) ? \$init{'$name'} :";
8cc95fdb	146	if( $type eq '@' ){
430530ea	147	$out .= " croak 'Initializer for $name must be array reference'\n";
	148	$out .= " if defined(\$init{'$name'}) && ref(\$init{'$name'}) ne 'ARRAY';\n";
	149	$out .= " \$r->$elem = $init [];$cmt\n";
8cc95fdb	150	$arrays{$name}++;
	151	}
	152	elsif( $type eq '%' ){
430530ea	153	$out .= " croak 'Initializer for $name must be hash reference'\n";
	154	$out .= " if defined(\$init{'$name'}) && ref(\$init{'$name'}) ne 'HASH';\n";
	155	$out .= " \$r->$elem = $init {};$cmt\n";
8cc95fdb	156	$hashes{$name}++;
	157	}
	158	elsif ( $type eq '$') {
430530ea	159	$out .= " \$r->$elem = $init undef;$cmt\n";
8cc95fdb	160	}
8cc95fdb	161	elsif( $type =~ /^\w+(?:::\w+)*$/ ){
430530ea	162	$init = "defined(\$init{'$name'}) ? \%{\$init{'$name'}} : ()";
	163	$out .= " croak 'Initializer for $name must be hash reference'\n";
	164	$out .= " if defined(\$init{'$name'}) && ref(\$init{'$name'}) ne 'HASH';\n";
	165	$out .= " \$r->$elem = '${type}'->new($init);$cmt\n";
8cc95fdb	166	$classes{$name} = $type;
	167	$got_class = 1;
	168	}
	169	else{
	170	croak "'$type' is not a valid struct element type";
	171	}
	172	$idx += 2;
	173	}
430530ea	174	$out .= " bless \$r, \$class;\n }\n";
8cc95fdb	175
	176	# Create accessor methods.
	177
8cc95fdb	178	my( $pre, $pst, $sel );
	179	$cnt = 0;
	180	foreach $name (@methods){
	181	if ( do { no strict 'refs'; defined &{$class . "::$name"} } ) {
7e6d00f8	182	warnings::warnif("function '$name' already defined, overrides struct accessor method");
8cc95fdb	183	}
	184	else {
	185	$pre = $pst = $cmt = $sel = '';
	186	if( defined $refs{$name} ){
	187	$pre = "\\(";
	188	$pst = ")";
	189	$cmt = " # returns ref";
	190	}
	191	$out .= " sub $name {$cmt\n my \$r = shift;\n";
	192	if( $base_type eq 'ARRAY' ){
	193	$elem = "[$cnt]";
	194	++$cnt;
	195	}
	196	elsif( $base_type eq 'HASH' ){
430530ea	197	$elem = "{'${class}::$name'}";
8cc95fdb	198	}
	199	if( defined $arrays{$name} ){
	200	$out .= " my \$i;\n";
430530ea	201	$out .= " \@_ ? (\$i = shift) : return \$r->$elem;\n";
8cc95fdb	202	$sel = "->[\$i]";
	203	}
	204	elsif( defined $hashes{$name} ){
	205	$out .= " my \$i;\n";
430530ea	206	$out .= " \@_ ? (\$i = shift) : return \$r->$elem;\n";
8cc95fdb	207	$sel = "->{\$i}";
	208	}
	209	elsif( defined $classes{$name} ){
	210	if ( $CHECK_CLASS_MEMBERSHIP ) {
20408e3c	211	$out .= " croak '$name argument is wrong class' if \@_ && ! UNIVERSAL::isa(\$_[0], '$classes{$name}');\n";
8cc95fdb	212	}
	213	}
	214	$out .= " croak 'Too many args to $name' if \@_ > 1;\n";
	215	$out .= " \@_ ? ($pre\$r->$elem$sel = shift$pst) : $pre\$r->$elem$sel$pst;\n";
	216	$out .= " }\n";
	217	}
	218	}
	219	$out .= "}\n1;\n";
	220
	221	print $out if $print;
	222	my $result = eval $out;
	223	carp $@ if $@;
	224	}
	225
	226	sub _usage_error {
	227	confess "struct usage error";
	228	}
	229
	230	sub _subclass_error {
	231	croak 'struct class cannot be a subclass (@ISA not allowed)';
	232	}
	233
	234	1; # for require
	235
	236
	237	__END__
	238
	239	=head1 NAME
	240
	241	Class::Struct - declare struct-like datatypes as Perl classes
	242
	243	=head1 SYNOPSIS
	244
	245	use Class::Struct;
	246	# declare struct, based on array:
	247	struct( CLASS_NAME => [ ELEMENT_NAME => ELEMENT_TYPE, ... ]);
	248	# declare struct, based on hash:
	249	struct( CLASS_NAME => { ELEMENT_NAME => ELEMENT_TYPE, ... });
	250
	251	package CLASS_NAME;
	252	use Class::Struct;
	253	# declare struct, based on array, implicit class name:
	254	struct( ELEMENT_NAME => ELEMENT_TYPE, ... );
	255
ab6e6725	256	# Declare struct at compile time
	257	use Class::Struct CLASS_NAME => [ ELEMENT_NAME => ELEMENT_TYPE, ... ];
	258	use Class::Struct CLASS_NAME => { ELEMENT_NAME => ELEMENT_TYPE, ... };
	259
8cc95fdb	260	package Myobj;
	261	use Class::Struct;
	262	# declare struct with four types of elements:
	263	struct( s => '$', a => '@', h => '%', c => 'My_Other_Class' );
	264
	265	$obj = new Myobj; # constructor
	266
	267	# scalar type accessor:
	268	$element_value = $obj->s; # element value
	269	$obj->s('new value'); # assign to element
	270
	271	# array type accessor:
	272	$ary_ref = $obj->a; # reference to whole array
	273	$ary_element_value = $obj->a(2); # array element value
	274	$obj->a(2, 'new value'); # assign to array element
	275
	276	# hash type accessor:
	277	$hash_ref = $obj->h; # reference to whole hash
	278	$hash_element_value = $obj->h('x'); # hash element value
ad6edfcb	279	$obj->h('x', 'new value'); # assign to hash element
8cc95fdb	280
	281	# class type accessor:
	282	$element_value = $obj->c; # object reference
	283	$obj->c->method(...); # call method of object
	284	$obj->c(new My_Other_Class); # assign a new object
	285
8cc95fdb	286	=head1 DESCRIPTION
	287
	288	C<Class::Struct> exports a single function, C<struct>.
	289	Given a list of element names and types, and optionally
	290	a class name, C<struct> creates a Perl 5 class that implements
	291	a "struct-like" data structure.
	292
	293	The new class is given a constructor method, C<new>, for creating
	294	struct objects.
	295
	296	Each element in the struct data has an accessor method, which is
	297	used to assign to the element and to fetch its value. The
	298	default accessor can be overridden by declaring a C<sub> of the
	299	same name in the package. (See Example 2.)
	300
	301	Each element's type can be scalar, array, hash, or class.
	302
8cc95fdb	303	=head2 The C<struct()> function
	304
	305	The C<struct> function has three forms of parameter-list.
	306
	307	struct( CLASS_NAME => [ ELEMENT_LIST ]);
	308	struct( CLASS_NAME => { ELEMENT_LIST });
	309	struct( ELEMENT_LIST );
	310
	311	The first and second forms explicitly identify the name of the
	312	class being created. The third form assumes the current package
	313	name as the class name.
	314
	315	An object of a class created by the first and third forms is
	316	based on an array, whereas an object of a class created by the
	317	second form is based on a hash. The array-based forms will be
	318	somewhat faster and smaller; the hash-based forms are more
	319	flexible.
	320
	321	The class created by C<struct> must not be a subclass of another
	322	class other than C<UNIVERSAL>.
	323
430530ea	324	It can, however, be used as a superclass for other classes. To facilitate
	325	this, the generated constructor method uses a two-argument blessing.
	326	Furthermore, if the class is hash-based, the key of each element is
	327	prefixed with the class name (see I<Perl Cookbook>, Recipe 13.12).
	328
8cc95fdb	329	A function named C<new> must not be explicitly defined in a class
	330	created by C<struct>.
	331
	332	The I<ELEMENT_LIST> has the form
	333
	334	NAME => TYPE, ...
	335
	336	Each name-type pair declares one element of the struct. Each
	337	element name will be defined as an accessor method unless a
	338	method by that name is explicitly defined; in the latter case, a
103ff8e3	339	warning is issued if the warning flag (B<-w>) is set.
8cc95fdb	340
ab6e6725	341	=head2 Class Creation at Compile Time
	342
	343	C<Class::Struct> can create your class at compile time. The main reason
	344	for doing this is obvious, so your class acts like every other class in
	345	Perl. Creating your class at compile time will make the order of events
	346	similar to using any other class ( or Perl module ).
	347
	348	There is no significant speed gain between compile time and run time
	349	class creation, there is just a new, more standard order of events.
8cc95fdb	350
	351	=head2 Element Types and Accessor Methods
	352
	353	The four element types -- scalar, array, hash, and class -- are
	354	represented by strings -- C<'$'>, C<'@'>, C<'%'>, and a class name --
	355	optionally preceded by a C<'*'>.
	356
	357	The accessor method provided by C<struct> for an element depends
	358	on the declared type of the element.
	359
	360	=over
	361
	362	=item Scalar (C<'$'> or C<'*$'>)
	363
430530ea	364	The element is a scalar, and by default is initialized to C<undef>
430530ea	365	(but see L<Initializing with new>).
8cc95fdb	366
	367	The accessor's argument, if any, is assigned to the element.
	368
	369	If the element type is C<'$'>, the value of the element (after
	370	assignment) is returned. If the element type is C<'*$'>, a reference
	371	to the element is returned.
	372
	373	=item Array (C<'@'> or C<'*@'>)
	374
430530ea	375	The element is an array, initialized by default to C<()>.
8cc95fdb	376
8cc95fdb	377	With no argument, the accessor returns a reference to the
430530ea	378	element's whole array (whether or not the element was
58231d39	379	specified as C<'@'> or C<'*@'>).
8cc95fdb	380
	381	With one or two arguments, the first argument is an index
	382	specifying one element of the array; the second argument, if
	383	present, is assigned to the array element. If the element type
	384	is C<'@'>, the accessor returns the array element value. If the
	385	element type is C<'*@'>, a reference to the array element is
	386	returned.
	387
	388	=item Hash (C<'%'> or C<'*%'>)
	389
430530ea	390	The element is a hash, initialized by default to C<()>.
8cc95fdb	391
8cc95fdb	392	With no argument, the accessor returns a reference to the
430530ea	393	element's whole hash (whether or not the element was
58231d39	394	specified as C<'%'> or C<'*%'>).
8cc95fdb	395
	396	With one or two arguments, the first argument is a key specifying
	397	one element of the hash; the second argument, if present, is
	398	assigned to the hash element. If the element type is C<'%'>, the
	399	accessor returns the hash element value. If the element type is
	400	C<'*%'>, a reference to the hash element is returned.
	401
	402	=item Class (C<'Class_Name'> or C<'*Class_Name'>)
	403
	404	The element's value must be a reference blessed to the named
	405	class or to one of its subclasses. The element is initialized to
	406	the result of calling the C<new> constructor of the named class.
	407
	408	The accessor's argument, if any, is assigned to the element. The
	409	accessor will C<croak> if this is not an appropriate object
	410	reference.
	411
	412	If the element type does not start with a C<'*'>, the accessor
	413	returns the element value (after assignment). If the element type
	414	starts with a C<'*'>, a reference to the element itself is returned.
	415
	416	=back
	417
430530ea	418	=head2 Initializing with C<new>
	419
	420	C<struct> always creates a constructor called C<new>. That constructor
	421	may take a list of initializers for the various elements of the new
	422	struct.
	423
	424	Each initializer is a pair of values: I<element name>C< =E<gt> >I<value>.
	425	The initializer value for a scalar element is just a scalar value. The
	426	initializer for an array element is an array reference. The initializer
	427	for a hash is a hash reference.
	428
	429	The initializer for a class element is also a hash reference, and the
	430	contents of that hash are passed to the element's own constructor.
	431
	432	See Example 3 below for an example of initialization.
	433
8cc95fdb	434	=head1 EXAMPLES
	435
	436	=over
	437
	438	=item Example 1
	439
	440	Giving a struct element a class type that is also a struct is how
	441	structs are nested. Here, C<timeval> represents a time (seconds and
	442	microseconds), and C<rusage> has two elements, each of which is of
	443	type C<timeval>.
	444
	445	use Class::Struct;
	446
	447	struct( rusage => {
	448	ru_utime => timeval, # seconds
	449	ru_stime => timeval, # microseconds
	450	});
	451
	452	struct( timeval => [
	453	tv_secs => '$',
	454	tv_usecs => '$',
	455	]);
	456
	457	# create an object:
	458	my $t = new rusage;
8cc95fdb	459
430530ea	460	# $t->ru_utime and $t->ru_stime are objects of type timeval.
8cc95fdb	461	# set $t->ru_utime to 100.0 sec and $t->ru_stime to 5.0 sec.
	462	$t->ru_utime->tv_secs(100);
	463	$t->ru_utime->tv_usecs(0);
	464	$t->ru_stime->tv_secs(5);
	465	$t->ru_stime->tv_usecs(0);
	466
8cc95fdb	467	=item Example 2
	468
	469	An accessor function can be redefined in order to provide
	470	additional checking of values, etc. Here, we want the C<count>
	471	element always to be nonnegative, so we redefine the C<count>
	472	accessor accordingly.
	473
	474	package MyObj;
	475	use Class::Struct;
	476
430530ea	477	# declare the struct
8cc95fdb	478	struct ( 'MyObj', { count => '$', stuff => '%' } );
8cc95fdb	479
430530ea	480	# override the default accessor method for 'count'
8cc95fdb	481	sub count {
	482	my $self = shift;
	483	if ( @_ ) {
	484	die 'count must be nonnegative' if $_[0] < 0;
	485	$self->{'count'} = shift;
	486	warn "Too many args to count" if @_;
	487	}
	488	return $self->{'count'};
	489	}
	490
	491	package main;
	492	$x = new MyObj;
	493	print "\$x->count(5) = ", $x->count(5), "\n";
	494	# prints '$x->count(5) = 5'
	495
	496	print "\$x->count = ", $x->count, "\n";
	497	# prints '$x->count = 5'
	498
	499	print "\$x->count(-5) = ", $x->count(-5), "\n";
	500	# dies due to negative argument!
	501
430530ea	502	=item Example 3
	503
	504	The constructor of a generated class can be passed a list
	505	of I<element>=>I<value> pairs, with which to initialize the struct.
	506	If no initializer is specified for a particular element, its default
	507	initialization is performed instead. Initializers for non-existent
	508	elements are silently ignored.
	509
	510	Note that the initializer for a nested struct is specified
	511	as an anonymous hash of initializers, which is passed on to the nested
	512	struct's constructor.
	513
430530ea	514	use Class::Struct;
	515
	516	struct Breed =>
	517	{
	518	name => '$',
	519	cross => '$',
	520	};
	521
	522	struct Cat =>
	523	[
	524	name => '$',
	525	kittens => '@',
	526	markings => '%',
	527	breed => 'Breed',
	528	];
	529
	530
	531	my $cat = Cat->new( name => 'Socks',
	532	kittens => ['Monica', 'Kenneth'],
	533	markings => { socks=>1, blaze=>"white" },
	534	breed => { name=>'short-hair', cross=>1 },
	535	);
	536
	537	print "Once a cat called ", $cat->name, "\n";
	538	print "(which was a ", $cat->breed->name, ")\n";
	539	print "had two kittens: ", join(' and ', @{$cat->kittens}), "\n";
	540
a45bd81d	541	=back
8cc95fdb	542
	543	=head1 Author and Modification History
	544
ab6e6725	545	Modified by Casey Tweten, 2000-11-08, v0.59.
	546
	547	Added the ability for compile time class creation.
	548
430530ea	549	Modified by Damian Conway, 1999-03-05, v0.58.
	550
	551	Added handling of hash-like arg list to class ctor.
	552
	553	Changed to two-argument blessing in ctor to support
	554	derivation from created classes.
	555
	556	Added classname prefixes to keys in hash-based classes
	557	(refer to "Perl Cookbook", Recipe 13.12 for rationale).
	558
	559	Corrected behaviour of accessors for '@' and '%' struct
	560	elements. Package now implements documented behaviour when
	561	returning a reference to an entire hash or array element.
	562	Previously these were returned as a reference to a reference
	563	to the element.
	564
8cc95fdb	565	Renamed to C<Class::Struct> and modified by Jim Miner, 1997-04-02.
	566
	567	members() function removed.
	568	Documentation corrected and extended.
	569	Use of struct() in a subclass prohibited.
	570	User definition of accessor allowed.
	571	Treatment of '*' in element types corrected.
	572	Treatment of classes as element types corrected.
	573	Class name to struct() made optional.
	574	Diagnostic checks added.
	575
8cc95fdb	576	Originally C<Class::Template> by Dean Roehrich.
	577
	578	# Template.pm --- struct/member template builder
	579	# 12mar95
	580	# Dean Roehrich
	581	#
	582	# changes/bugs fixed since 28nov94 version:
	583	# - podified
	584	# changes/bugs fixed since 21nov94 version:
	585	# - Fixed examples.
	586	# changes/bugs fixed since 02sep94 version:
	587	# - Moved to Class::Template.
	588	# changes/bugs fixed since 20feb94 version:
	589	# - Updated to be a more proper module.
	590	# - Added "use strict".
	591	# - Bug in build_methods, was using @var when @$var needed.
	592	# - Now using my() rather than local().
	593	#
	594	# Uses perl5 classes to create nested data types.
	595	# This is offered as one implementation of Tom Christiansen's "structs.pl"
	596	# idea.
	597
	598	=cut