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+package Class::Struct;
+
+## See POD after __END__
+
+require 5.002;
+
+use strict;
+use vars qw(@ISA @EXPORT);
+
+use Carp;
+
+require Exporter;
+@ISA = qw(Exporter);
+@EXPORT = qw(struct);
+
+## 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 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";
+
+ 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' ){
+ $elem = "{'$name'}";
+ }
+ elsif( $base_type eq 'ARRAY' ){
+ $elem = "[$cnt]";
+ ++$cnt;
+ $cmt = " # $name";
+ }
+ if( $type =~ /^\*(.)/ ){
+ $refs{$name}++;
+ $type = $1;
+ }
+ if( $type eq '@' ){
+ $out .= " \$r->$elem = [];$cmt\n";
+ $arrays{$name}++;
+ }
+ elsif( $type eq '%' ){
+ $out .= " \$r->$elem = {};$cmt\n";
+ $hashes{$name}++;
+ }
+ elsif ( $type eq '$') {
+ $out .= " \$r->$elem = undef;$cmt\n";
+ }
+ elsif( $type =~ /^\w+(?:::\w+)*$/ ){
+ $out .= " \$r->$elem = '${type}'->new();$cmt\n";
+ $classes{$name} = $type;
+ $got_class = 1;
+ }
+ else{
+ croak "'$type' is not a valid struct element type";
+ }
+ $idx += 2;
+ }
+ $out .= " bless \$r;\n }\n";
+
+ # Create accessor methods.
+
+ if ( $got_class && $CHECK_CLASS_MEMBERSHIP ) {
+ $out .= " use UNIVERSAL;\n";
+ }
+ my( $pre, $pst, $sel );
+ $cnt = 0;
+ foreach $name (@methods){
+ if ( do { no strict 'refs'; defined &{$class . "::$name"} } ) {
+ carp "function '$name' already defined, overrides struct accessor method"
+ if $^W;
+ }
+ 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' ){
+ $elem = "{'$name'}";
+ }
+ if( defined $arrays{$name} ){
+ $out .= " my \$i;\n";
+ $out .= " \@_ ? (\$i = shift) : return $pre\$r->$elem$pst;\n";
+ $sel = "->[\$i]";
+ }
+ elsif( defined $hashes{$name} ){
+ $out .= " my \$i;\n";
+ $out .= " \@_ ? (\$i = shift) : return $pre\$r->$elem$pst;\n";
+ $sel = "->{\$i}";
+ }
+ elsif( defined $classes{$name} ){
+ if ( $CHECK_CLASS_MEMBERSHIP ) {
+ $out .= " croak '$name argument is wrong class' if \@_ && ! UNIVERSAL::isa(\$_[0], '$type');\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
+ $obj->c(new My_Other_Class); # assign a new object
+
+
+=head1 DESCRIPTION
+
+C<Class::Struct> exports a single function, C<struct>.
+Given a list of element names and types, and optionally
+a class name, C<struct> creates a Perl 5 class that implements
+a "struct-like" data structure.
+
+The new class is given a constructor method, C<new>, for creating
+struct objects.
+
+Each element in the struct data has an accessor method, which is
+used to assign to the element and to fetch its value. The
+default accessor can be overridden by declaring a C<sub> of the
+same name in the package. (See Example 2.)
+
+Each element's type can be scalar, array, hash, or class.
+
+
+=head2 The C<struct()> function
+
+The C<struct> function has three forms of parameter-list.
+
+ struct( CLASS_NAME => [ ELEMENT_LIST ]);
+ struct( CLASS_NAME => { ELEMENT_LIST });
+ struct( ELEMENT_LIST );
+
+The first and second forms explicitly identify the name of the
+class being created. The third form assumes the current package
+name as the class name.
+
+An object of a class created by the first and third forms is
+based on an array, whereas an object of a class created by the
+second form is based on a hash. The array-based forms will be
+somewhat faster and smaller; the hash-based forms are more
+flexible.
+
+The class created by C<struct> must not be a subclass of another
+class other than C<UNIVERSAL>.
+
+A function named C<new> must not be explicitly defined in a class
+created by C<struct>.
+
+The I<ELEMENT_LIST> has the form
+
+ NAME => TYPE, ...
+
+Each name-type pair declares one element of the struct. Each
+element name will be defined as an accessor method unless a
+method by that name is explicitly defined; in the latter case, a
+warning is issued if the warning flag (-w) is set.
+
+
+=head2 Element Types and Accessor Methods
+
+The four element types -- scalar, array, hash, and class -- are
+represented by strings -- C<'$'>, 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 is initialized to C<undef>.
+
+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 to C<()>.
+
+With no argument, the accessor returns a reference to the
+element's whole array.
+
+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 to C<()>.
+
+With no argument, the accessor returns a reference to the
+element's whole hash.
+
+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
+
+=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) = ", $x->count(-5), "\n";
+ # dies due to negative argument!
+
+
+=head1 Author and Modification History
+
+
+Renamed to C<Class::Struct> and modified by Jim Miner, 1997-04-02.
+
+ members() function removed.
+ Documentation corrected and extended.
+ Use of struct() in a subclass prohibited.
+ User definition of accessor allowed.
+ Treatment of '*' in element types corrected.
+ Treatment of classes as element types corrected.
+ Class name to struct() made optional.
+ Diagnostic checks added.
+
+
+Originally C<Class::Template> by Dean Roehrich.
+
+ # Template.pm --- struct/member template builder
+ # 12mar95
+ # Dean Roehrich
+ #
+ # changes/bugs fixed since 28nov94 version:
+ # - podified
+ # changes/bugs fixed since 21nov94 version:
+ # - Fixed examples.
+ # changes/bugs fixed since 02sep94 version:
+ # - Moved to Class::Template.
+ # changes/bugs fixed since 20feb94 version:
+ # - Updated to be a more proper module.
+ # - Added "use strict".
+ # - Bug in build_methods, was using @var when @$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
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