[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 = '0.61';

## 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'} : undef";
            $out .= "    croak 'Initializer for $name must be $type reference'\n";
            $out .= "        if defined(\$init{'$name'}) && !UNIVERSAL::isa(\$init{'$name'}, '$type');\n";
            $out .= "    \$r->$elem = $init;$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"; 
                $out .= "    if (ref(\$i) eq 'ARRAY' && !\@_) { \$r->$elem = \$i; return \$r }\n";
                $sel = "->[\$i]";
            }
            elsif( defined $hashes{$name} ){
                $out .= "    my \$i;\n";
                $out .= "    \@_ ? (\$i = shift) : return \$r->$elem;\n";
                $out .= "    if (ref(\$i) eq 'HASH' && !\@_) { \$r->$elem = \$i; return \$r }\n";
                $sel = "->{\$i}";
            }
            elsif( defined $classes{$name} ){
                if ( $CHECK_CLASS_MEMBERSHIP ) {
                    $out .= "    croak '$name argument is wrong class' if \@_ && ! UNIVERSAL::isa(\$_[0], '$classes{$name}');\n";
                }
            }
            $out .= "    croak 'Too many args to $name' if \@_ > 1;\n";
            $out .= "    \@_ ? ($pre\$r->$elem$sel = shift$pst) : $pre\$r->$elem$sel$pst;\n";
            $out .= "  }\n";
        }
    }
    $out .= "}\n1;\n";

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

sub _usage_error {
    confess "struct usage error";
}

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

1; # for require


__END__

=head1 NAME

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

=head1 SYNOPSIS

    use Class::Struct;
            # declare struct, based on array:
    struct( CLASS_NAME => [ ELEMENT_NAME => ELEMENT_TYPE, ... ]);
            # declare struct, based on hash:
    struct( CLASS_NAME => { ELEMENT_NAME => ELEMENT_TYPE, ... });

    package CLASS_NAME;
    use Class::Struct;
            # declare struct, based on array, implicit class name:
    struct( ELEMENT_NAME => ELEMENT_TYPE, ... );

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

    package Myobj;
    use Class::Struct;
            # declare struct with four types of elements:
    struct( s => '$', a => '@', h => '%', c => 'My_Other_Class' );

    $obj = new Myobj;               # constructor

                                    # scalar type accessor:
    $element_value = $obj->s;           # element value
    $obj->s('new value');               # assign to element

                                    # array type accessor:
    $ary_ref = $obj->a;                 # reference to whole array
    $ary_element_value = $obj->a(2);    # array element value
    $obj->a(2, 'new value');            # assign to array element

                                    # hash type accessor:
    $hash_ref = $obj->h;                # reference to whole hash
    $hash_element_value = $obj->h('x'); # hash element value
    $obj->h('x', 'new value');          # assign to hash element

                                    # class type accessor:
    $element_value = $obj->c;           # object reference
    $obj->c->method(...);               # call method of object
    $obj->c(new My_Other_Class);        # assign a new object

=head1 DESCRIPTION

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

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

Each element in the struct data has an accessor method, which is
used to assign to the element and to fetch its value.  The
default accessor can be overridden by declaring a C<sub> of the
same name in the package.  (See Example 2.)

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

=head2 The C<struct()> function

The C<struct> function has three forms of parameter-list.

    struct( CLASS_NAME => [ ELEMENT_LIST ]);
    struct( CLASS_NAME => { ELEMENT_LIST });
    struct( ELEMENT_LIST );

The first and second forms explicitly identify the name of the
class being created.  The third form assumes the current package
name as the class name.

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

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

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

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

The I<ELEMENT_LIST> has the form

    NAME => TYPE, ...

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

=head2 Class Creation at Compile Time

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

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

=head2 Element Types and Accessor Methods

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

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

=over 4

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

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

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

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

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

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

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

With one or two arguments, the first argument is an index
specifying one element of the array; the second argument, if
present, is assigned to the array element.  If the element type
is C<'@'>, the accessor returns the array element value.  If the
element type is C<'*@'>, a reference to the array element is
returned.

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

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

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

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

With one or two arguments, the first argument is a key specifying
one element of the hash; the second argument, if present, is
assigned to the hash element.  If the element type is C<'%'>, the
accessor returns the hash element value.  If the element type is
C<'*%'>, a reference to the hash element is returned.

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

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

The element's value must be a reference blessed to the named
class or to one of its subclasses. The element is 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 an object of the corresponding class,
(or of one of its subclasses).

See Example 3 below for an example of initialization.

=head1 EXAMPLES

=over 4

=item Example 1

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

    use Class::Struct;

    struct( rusage => {
        ru_utime => timeval,  # 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    => Breed->new(name=>'short-hair', cross=>1),
                      );

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

=back

=head1 Author and Modification History

Modified by Damian Conway, 2001-09-04, v0.61.

   Removed implicit construction of nested objects.
   This helpfulness was fraught with problems:
       * the class's constructor might not be called 'new'
       * the class might not have a no-argument constructor
       * "recursive" data structures don't work well:
                 package Person;
                 struct { mother => 'Person', father => 'Person'};
   It is now necessary to pass an object reference to initialize a
   nested object.


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

    Added the ability for compile time class creation.

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

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

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

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

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

Renamed to C<Class::Struct> and modified by Jim Miner, 1997-04-02.

    members() function removed.
    Documentation corrected and extended.
    Use of struct() in a subclass prohibited.
    User definition of accessor allowed.
    Treatment of '*' in element types corrected.
    Treatment of classes as element types corrected.
    Class name to struct() made optional.
    Diagnostic checks added.

Originally C<Class::Template> by Dean Roehrich.

    # Template.pm   --- struct/member template builder
    #   12mar95
    #   Dean Roehrich
    #
    # changes/bugs fixed since 28nov94 version:
    #  - podified
    # changes/bugs fixed since 21nov94 version:
    #  - Fixed examples.
    # changes/bugs fixed since 02sep94 version:
    #  - Moved to Class::Template.
    # changes/bugs fixed since 20feb94 version:
    #  - Updated to be a more proper module.
    #  - Added "use strict".
    #  - Bug in build_methods, was using @var when @$var needed.
    #  - Now using my() rather than local().
    #
    # Uses perl5 classes to create nested data types.
    # This is offered as one implementation of Tom Christiansen's "structs.pl"
    # idea.

=cut
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
f8aada62	17	$VERSION = '0.61';
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
22633ac4	57	if ( @_ == 0 ) {
ab6e6725	58	$self->export_to_level( 1, $self, @EXPORT );
22633ac4	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, $self, @_ );
	63	} else {
	64	&struct;
ab6e6725	65	}
	66	}
	67
8cc95fdb	68	sub struct {
	69
	70	# Determine parameter list structure, one of:
	71	# struct( class => [ element-list ])
	72	# struct( class => { element-list })
	73	# struct( element-list )
	74	# Latter form assumes current package name as struct name.
	75
	76	my ($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	}
ad6edfcb	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( $type =~ /^\w+(?:::\w+)*$/ ){
f8aada62	166	$init = "defined(\$init{'$name'}) ? \$init{'$name'} : undef";
	167	$out .= " croak 'Initializer for $name must be $type reference'\n";
	168	$out .= " if defined(\$init{'$name'}) && !UNIVERSAL::isa(\$init{'$name'}, '$type');\n";
	169	$out .= " \$r->$elem = $init;$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 . "::$name"} } ) {
7e6d00f8	186	warnings::warnif("function '$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";
726cfeaf	206	$out .= " if (ref(\$i) eq 'ARRAY' && !\@_) { \$r->$elem = \$i; return \$r }\n";
8cc95fdb	207	$sel = "->[\$i]";
	208	}
	209	elsif( defined $hashes{$name} ){
	210	$out .= " my \$i;\n";
726cfeaf	211	$out .= " \@_ ? (\$i = shift) : return \$r->$elem;\n";
726cfeaf	212	$out .= " if (ref(\$i) eq 'HASH' && !\@_) { \$r->$elem = \$i; return \$r }\n";
8cc95fdb	213	$sel = "->{\$i}";
	214	}
	215	elsif( defined $classes{$name} ){
	216	if ( $CHECK_CLASS_MEMBERSHIP ) {
20408e3c	217	$out .= " croak '$name argument is wrong class' if \@_ && ! UNIVERSAL::isa(\$_[0], '$classes{$name}');\n";
8cc95fdb	218	}
	219	}
	220	$out .= " croak 'Too many args to $name' if \@_ > 1;\n";
	221	$out .= " \@_ ? ($pre\$r->$elem$sel = shift$pst) : $pre\$r->$elem$sel$pst;\n";
	222	$out .= " }\n";
	223	}
	224	}
	225	$out .= "}\n1;\n";
	226
	227	print $out if $print;
	228	my $result = eval $out;
	229	carp $@ if $@;
	230	}
	231
	232	sub _usage_error {
	233	confess "struct usage error";
	234	}
	235
	236	sub _subclass_error {
	237	croak 'struct class cannot be a subclass (@ISA not allowed)';
	238	}
	239
	240	1; # for require
	241
	242
	243	__END__
	244
	245	=head1 NAME
	246
	247	Class::Struct - declare struct-like datatypes as Perl classes
	248
	249	=head1 SYNOPSIS
	250
	251	use Class::Struct;
	252	# declare struct, based on array:
	253	struct( CLASS_NAME => [ ELEMENT_NAME => ELEMENT_TYPE, ... ]);
	254	# declare struct, based on hash:
	255	struct( CLASS_NAME => { ELEMENT_NAME => ELEMENT_TYPE, ... });
	256
	257	package CLASS_NAME;
	258	use Class::Struct;
	259	# declare struct, based on array, implicit class name:
	260	struct( ELEMENT_NAME => ELEMENT_TYPE, ... );
	261
ab6e6725	262	# Declare struct at compile time
	263	use Class::Struct CLASS_NAME => [ ELEMENT_NAME => ELEMENT_TYPE, ... ];
	264	use Class::Struct CLASS_NAME => { ELEMENT_NAME => ELEMENT_TYPE, ... };
	265
8cc95fdb	266	package Myobj;
	267	use Class::Struct;
	268	# declare struct with four types of elements:
	269	struct( s => '$', a => '@', h => '%', c => 'My_Other_Class' );
	270
	271	$obj = new Myobj; # constructor
	272
	273	# scalar type accessor:
	274	$element_value = $obj->s; # element value
	275	$obj->s('new value'); # assign to element
	276
	277	# array type accessor:
	278	$ary_ref = $obj->a; # reference to whole array
	279	$ary_element_value = $obj->a(2); # array element value
	280	$obj->a(2, 'new value'); # assign to array element
	281
	282	# hash type accessor:
	283	$hash_ref = $obj->h; # reference to whole hash
	284	$hash_element_value = $obj->h('x'); # hash element value
ad6edfcb	285	$obj->h('x', 'new value'); # assign to hash element
8cc95fdb	286
	287	# class type accessor:
	288	$element_value = $obj->c; # object reference
	289	$obj->c->method(...); # call method of object
	290	$obj->c(new My_Other_Class); # assign a new object
	291
8cc95fdb	292	=head1 DESCRIPTION
	293
	294	C<Class::Struct> exports a single function, C<struct>.
	295	Given a list of element names and types, and optionally
	296	a class name, C<struct> creates a Perl 5 class that implements
	297	a "struct-like" data structure.
	298
	299	The new class is given a constructor method, C<new>, for creating
	300	struct objects.
	301
	302	Each element in the struct data has an accessor method, which is
	303	used to assign to the element and to fetch its value. The
	304	default accessor can be overridden by declaring a C<sub> of the
	305	same name in the package. (See Example 2.)
	306
	307	Each element's type can be scalar, array, hash, or class.
	308
8cc95fdb	309	=head2 The C<struct()> function
	310
	311	The C<struct> function has three forms of parameter-list.
	312
	313	struct( CLASS_NAME => [ ELEMENT_LIST ]);
	314	struct( CLASS_NAME => { ELEMENT_LIST });
	315	struct( ELEMENT_LIST );
	316
	317	The first and second forms explicitly identify the name of the
	318	class being created. The third form assumes the current package
	319	name as the class name.
	320
	321	An object of a class created by the first and third forms is
	322	based on an array, whereas an object of a class created by the
	323	second form is based on a hash. The array-based forms will be
	324	somewhat faster and smaller; the hash-based forms are more
	325	flexible.
	326
	327	The class created by C<struct> must not be a subclass of another
	328	class other than C<UNIVERSAL>.
	329
430530ea	330	It can, however, be used as a superclass for other classes. To facilitate
	331	this, the generated constructor method uses a two-argument blessing.
	332	Furthermore, if the class is hash-based, the key of each element is
	333	prefixed with the class name (see I<Perl Cookbook>, Recipe 13.12).
	334
8cc95fdb	335	A function named C<new> must not be explicitly defined in a class
	336	created by C<struct>.
	337
	338	The I<ELEMENT_LIST> has the form
	339
	340	NAME => TYPE, ...
	341
	342	Each name-type pair declares one element of the struct. Each
	343	element name will be defined as an accessor method unless a
	344	method by that name is explicitly defined; in the latter case, a
103ff8e3	345	warning is issued if the warning flag (B<-w>) is set.
8cc95fdb	346
ab6e6725	347	=head2 Class Creation at Compile Time
	348
	349	C<Class::Struct> can create your class at compile time. The main reason
	350	for doing this is obvious, so your class acts like every other class in
	351	Perl. Creating your class at compile time will make the order of events
	352	similar to using any other class ( or Perl module ).
	353
	354	There is no significant speed gain between compile time and run time
	355	class creation, there is just a new, more standard order of events.
8cc95fdb	356
	357	=head2 Element Types and Accessor Methods
	358
	359	The four element types -- scalar, array, hash, and class -- are
	360	represented by strings -- C<'$'>, C<'@'>, C<'%'>, and a class name --
	361	optionally preceded by a C<'*'>.
	362
	363	The accessor method provided by C<struct> for an element depends
	364	on the declared type of the element.
	365
bbc7dcd2	366	=over 4
8cc95fdb	367
	368	=item Scalar (C<'$'> or C<'*$'>)
	369
430530ea	370	The element is a scalar, and by default is initialized to C<undef>
430530ea	371	(but see L<Initializing with new>).
8cc95fdb	372
	373	The accessor's argument, if any, is assigned to the element.
	374
	375	If the element type is C<'$'>, the value of the element (after
	376	assignment) is returned. If the element type is C<'*$'>, a reference
	377	to the element is returned.
	378
	379	=item Array (C<'@'> or C<'*@'>)
	380
430530ea	381	The element is an array, initialized by default to C<()>.
8cc95fdb	382
8cc95fdb	383	With no argument, the accessor returns a reference to the
430530ea	384	element's whole array (whether or not the element was
58231d39	385	specified as C<'@'> or C<'*@'>).
8cc95fdb	386
	387	With one or two arguments, the first argument is an index
	388	specifying one element of the array; the second argument, if
	389	present, is assigned to the array element. If the element type
	390	is C<'@'>, the accessor returns the array element value. If the
	391	element type is C<'*@'>, a reference to the array element is
	392	returned.
	393
726cfeaf	394	As a special case, when the accessor is called with an array reference
	395	as the sole argument, this causes an assignment of the whole array element.
	396	The object reference is returned.
	397
8cc95fdb	398	=item Hash (C<'%'> or C<'*%'>)
8cc95fdb	399
430530ea	400	The element is a hash, initialized by default to C<()>.
8cc95fdb	401
8cc95fdb	402	With no argument, the accessor returns a reference to the
430530ea	403	element's whole hash (whether or not the element was
58231d39	404	specified as C<'%'> or C<'*%'>).
8cc95fdb	405
	406	With one or two arguments, the first argument is a key specifying
	407	one element of the hash; the second argument, if present, is
	408	assigned to the hash element. If the element type is C<'%'>, the
	409	accessor returns the hash element value. If the element type is
	410	C<'*%'>, a reference to the hash element is returned.
	411
726cfeaf	412	As a special case, when the accessor is called with a hash reference
	413	as the sole argument, this causes an assignment of the whole hash element.
	414	The object reference is returned.
	415
8cc95fdb	416	=item Class (C<'Class_Name'> or C<'*Class_Name'>)
	417
	418	The element's value must be a reference blessed to the named
	419	class or to one of its subclasses. The element is initialized to
	420	the result of calling the C<new> constructor of the named class.
	421
	422	The accessor's argument, if any, is assigned to the element. The
	423	accessor will C<croak> if this is not an appropriate object
	424	reference.
	425
	426	If the element type does not start with a C<'*'>, the accessor
	427	returns the element value (after assignment). If the element type
	428	starts with a C<'*'>, a reference to the element itself is returned.
	429
	430	=back
	431
430530ea	432	=head2 Initializing with C<new>
	433
	434	C<struct> always creates a constructor called C<new>. That constructor
	435	may take a list of initializers for the various elements of the new
	436	struct.
	437
	438	Each initializer is a pair of values: I<element name>C< =E<gt> >I<value>.
	439	The initializer value for a scalar element is just a scalar value. The
	440	initializer for an array element is an array reference. The initializer
	441	for a hash is a hash reference.
	442
f8aada62	443	The initializer for a class element is an object of the corresponding class,
f8aada62	444	(or of one of its subclasses).
430530ea	445
	446	See Example 3 below for an example of initialization.
	447
8cc95fdb	448	=head1 EXAMPLES
8cc95fdb	449
bbc7dcd2	450	=over 4
8cc95fdb	451
	452	=item Example 1
	453
	454	Giving a struct element a class type that is also a struct is how
	455	structs are nested. Here, C<timeval> represents a time (seconds and
	456	microseconds), and C<rusage> has two elements, each of which is of
	457	type C<timeval>.
	458
	459	use Class::Struct;
	460
	461	struct( rusage => {
	462	ru_utime => timeval, # seconds
	463	ru_stime => timeval, # microseconds
	464	});
	465
	466	struct( timeval => [
	467	tv_secs => '$',
	468	tv_usecs => '$',
	469	]);
	470
	471	# create an object:
	472	my $t = new rusage;
8cc95fdb	473
430530ea	474	# $t->ru_utime and $t->ru_stime are objects of type timeval.
8cc95fdb	475	# set $t->ru_utime to 100.0 sec and $t->ru_stime to 5.0 sec.
	476	$t->ru_utime->tv_secs(100);
	477	$t->ru_utime->tv_usecs(0);
	478	$t->ru_stime->tv_secs(5);
	479	$t->ru_stime->tv_usecs(0);
	480
8cc95fdb	481	=item Example 2
	482
	483	An accessor function can be redefined in order to provide
	484	additional checking of values, etc. Here, we want the C<count>
	485	element always to be nonnegative, so we redefine the C<count>
	486	accessor accordingly.
	487
	488	package MyObj;
	489	use Class::Struct;
	490
430530ea	491	# declare the struct
8cc95fdb	492	struct ( 'MyObj', { count => '$', stuff => '%' } );
8cc95fdb	493
430530ea	494	# override the default accessor method for 'count'
8cc95fdb	495	sub count {
	496	my $self = shift;
	497	if ( @_ ) {
	498	die 'count must be nonnegative' if $_[0] < 0;
	499	$self->{'count'} = shift;
	500	warn "Too many args to count" if @_;
	501	}
	502	return $self->{'count'};
	503	}
	504
	505	package main;
	506	$x = new MyObj;
	507	print "\$x->count(5) = ", $x->count(5), "\n";
	508	# prints '$x->count(5) = 5'
	509
	510	print "\$x->count = ", $x->count, "\n";
	511	# prints '$x->count = 5'
	512
	513	print "\$x->count(-5) = ", $x->count(-5), "\n";
	514	# dies due to negative argument!
	515
430530ea	516	=item Example 3
	517
	518	The constructor of a generated class can be passed a list
	519	of I<element>=>I<value> pairs, with which to initialize the struct.
	520	If no initializer is specified for a particular element, its default
	521	initialization is performed instead. Initializers for non-existent
	522	elements are silently ignored.
	523
	524	Note that the initializer for a nested struct is specified
	525	as an anonymous hash of initializers, which is passed on to the nested
	526	struct's constructor.
	527
430530ea	528	use Class::Struct;
	529
	530	struct Breed =>
	531	{
	532	name => '$',
	533	cross => '$',
	534	};
	535
	536	struct Cat =>
	537	[
	538	name => '$',
	539	kittens => '@',
	540	markings => '%',
	541	breed => 'Breed',
	542	];
	543
	544
	545	my $cat = Cat->new( name => 'Socks',
	546	kittens => ['Monica', 'Kenneth'],
	547	markings => { socks=>1, blaze=>"white" },
f8aada62	548	breed => Breed->new(name=>'short-hair', cross=>1),
430530ea	549	);
	550
	551	print "Once a cat called ", $cat->name, "\n";
	552	print "(which was a ", $cat->breed->name, ")\n";
	553	print "had two kittens: ", join(' and ', @{$cat->kittens}), "\n";
	554
a45bd81d	555	=back
8cc95fdb	556
	557	=head1 Author and Modification History
	558
f8aada62	559	Modified by Damian Conway, 2001-09-04, v0.61.
	560
	561	Removed implicit construction of nested objects.
	562	This helpfulness was fraught with problems:
	563	* the class's constructor might not be called 'new'
	564	* the class might not have a no-argument constructor
	565	* "recursive" data structures don't work well:
	566	package Person;
	567	struct { mother => 'Person', father => 'Person'};
	568	It is now necessary to pass an object reference to initialize a
	569	nested object.
	570
	571
e1e60e72	572	Modified by Casey West, 2000-11-08, v0.59.
ab6e6725	573
	574	Added the ability for compile time class creation.
	575
430530ea	576	Modified by Damian Conway, 1999-03-05, v0.58.
	577
	578	Added handling of hash-like arg list to class ctor.
	579
	580	Changed to two-argument blessing in ctor to support
	581	derivation from created classes.
	582
	583	Added classname prefixes to keys in hash-based classes
	584	(refer to "Perl Cookbook", Recipe 13.12 for rationale).
	585
	586	Corrected behaviour of accessors for '@' and '%' struct
	587	elements. Package now implements documented behaviour when
	588	returning a reference to an entire hash or array element.
	589	Previously these were returned as a reference to a reference
	590	to the element.
	591
8cc95fdb	592	Renamed to C<Class::Struct> and modified by Jim Miner, 1997-04-02.
	593
	594	members() function removed.
	595	Documentation corrected and extended.
	596	Use of struct() in a subclass prohibited.
	597	User definition of accessor allowed.
	598	Treatment of '*' in element types corrected.
	599	Treatment of classes as element types corrected.
	600	Class name to struct() made optional.
	601	Diagnostic checks added.
	602
8cc95fdb	603	Originally C<Class::Template> by Dean Roehrich.
	604
	605	# Template.pm --- struct/member template builder
	606	# 12mar95
	607	# Dean Roehrich
	608	#
	609	# changes/bugs fixed since 28nov94 version:
	610	# - podified
	611	# changes/bugs fixed since 21nov94 version:
	612	# - Fixed examples.
	613	# changes/bugs fixed since 02sep94 version:
	614	# - Moved to Class::Template.
	615	# changes/bugs fixed since 20feb94 version:
	616	# - Updated to be a more proper module.
	617	# - Added "use strict".
	618	# - Bug in build_methods, was using @var when @$var needed.
	619	# - Now using my() rather than local().
	620	#
	621	# Uses perl5 classes to create nested data types.
	622	# This is offered as one implementation of Tom Christiansen's "structs.pl"
	623	# idea.
	624
	625	=cut