{
package Foo;
- use fields qw(foo bar baz);
+ use fields qw(foo bar _Foo_private);
+ sub new {
+ my Foo $self = shift;
+ unless (ref $self) {
+ $self = fields::new($self);
+ $self->{_Foo_private} = "this is Foo's secret";
+ }
+ $self->{foo} = 10;
+ $self->{bar} = 20;
+ return $self;
+ }
}
- ...
- my Foo $var = new Foo;
+
+ my Foo $var = Foo::->new;
$var->{foo} = 42;
- # This will generate a compile-time error.
+ # this will generate a compile-time error
$var->{zap} = 42;
+ # subclassing
+ {
+ package Bar;
+ use base 'Foo';
+ use fields qw(baz _Bar_private); # not shared with Foo
+ sub new {
+ my $class = shift;
+ my $self = fields::new($class);
+ $self->SUPER::new(); # init base fields
+ $self->{baz} = 10; # init own fields
+ $self->{_Bar_private} = "this is Bar's secret";
+ return $self;
+ }
+ }
+
=head1 DESCRIPTION
The C<fields> pragma enables compile-time verified class fields.
+NOTE: The current implementation keeps the declared fields in the %FIELDS
+hash of the calling package, but this may change in future versions.
+Do B<not> update the %FIELDS hash directly, because it must be created
+at compile-time for it to be fully useful, as is done by this pragma.
+
+If a typed lexical variable holding a reference is used to access a
+hash element and a package with the same name as the type has declared
+class fields using this pragma, then the operation is turned into an
+array access at compile time.
+
+The related C<base> pragma will combine fields from base classes and any
+fields declared using the C<fields> pragma. This enables field
+inheritance to work properly.
+
+Field names that start with an underscore character are made private to
+the class and are not visible to subclasses. Inherited fields can be
+overridden but will generate a warning if used together with the C<-w>
+switch.
+
+The effect of all this is that you can have objects with named fields
+which are as compact and as fast arrays to access. This only works
+as long as the objects are accessed through properly typed variables.
+If the objects are not typed, access is only checked at run time.
+
+The following functions are supported:
+
+=over 8
+
+=item new
+
+fields::new() creates and blesses a pseudo-hash comprised of the fields
+declared using the C<fields> pragma into the specified class.
+This makes it possible to write a constructor like this:
+
+ package Critter::Sounds;
+ use fields qw(cat dog bird);
+
+ sub new {
+ my Critter::Sounds $self = shift;
+ $self = fields::new($self) unless ref $self;
+ $self->{cat} = 'meow'; # scalar element
+ @$self{'dog','bird'} = ('bark','tweet'); # slice
+ return $self;
+ }
+
+=item phash
+
+fields::phash() can be used to create and initialize a plain (unblessed)
+pseudo-hash. This function should always be used instead of creating
+pseudo-hashes directly.
+
+If the first argument is a reference to an array, the pseudo-hash will
+be created with keys from that array. If a second argument is supplied,
+it must also be a reference to an array whose elements will be used as
+the values. If the second array contains less elements than the first,
+the trailing elements of the pseudo-hash will not be initialized.
+This makes it particularly useful for creating a pseudo-hash from
+subroutine arguments:
+
+ sub dogtag {
+ my $tag = fields::phash([qw(name rank ser_num)], [@_]);
+ }
+
+fields::phash() also accepts a list of key-value pairs that will
+be used to construct the pseudo hash. Examples:
+
+ my $tag = fields::phash(name => "Joe",
+ rank => "captain",
+ ser_num => 42);
+
+ my $pseudohash = fields::phash(%args);
+
+=back
+
+=head1 SEE ALSO
+
+L<base>,
+L<perlref/Pseudo-hashes: Using an array as a hash>
+
=cut
+use 5.006_001;
+use strict;
+no strict 'refs';
+use warnings::register;
+our(%attr, $VERSION);
+
+$VERSION = "1.02";
+
+# some constants
+sub _PUBLIC () { 1 }
+sub _PRIVATE () { 2 }
+
+# The %attr hash holds the attributes of the currently assigned fields
+# per class. The hash is indexed by class names and the hash value is
+# an array reference. The first element in the array is the lowest field
+# number not belonging to a base class. The remaining elements' indices
+# are the field numbers. The values are integer bit masks, or undef
+# in the case of base class private fields (which occupy a slot but are
+# otherwise irrelevant to the class).
+
sub import {
my $class = shift;
- my ($package) = caller;
+ return unless @_;
+ my $package = caller(0);
+ # avoid possible typo warnings
+ %{"$package\::FIELDS"} = () unless %{"$package\::FIELDS"};
my $fields = \%{"$package\::FIELDS"};
- my $i = $fields->{__MAX__};
+ my $fattr = ($attr{$package} ||= [1]);
+ my $next = @$fattr;
+
+ if ($next > $fattr->[0]
+ and ($fields->{$_[0]} || 0) >= $fattr->[0])
+ {
+ # There are already fields not belonging to base classes.
+ # Looks like a possible module reload...
+ $next = $fattr->[0];
+ }
foreach my $f (@_) {
- if (defined($fields->{$f})) {
+ my $fno = $fields->{$f};
+
+ # Allow the module to be reloaded so long as field positions
+ # have not changed.
+ if ($fno and $fno != $next) {
+ require Carp;
+ if ($fno < $fattr->[0]) {
+ warnings::warnif("Hides field '$f' in base class") ;
+ } else {
+ Carp::croak("Field name '$f' already in use");
+ }
+ }
+ $fields->{$f} = $next;
+ $fattr->[$next] = ($f =~ /^_/) ? _PRIVATE : _PUBLIC;
+ $next += 1;
+ }
+ if (@$fattr > $next) {
+ # Well, we gave them the benefit of the doubt by guessing the
+ # module was reloaded, but they appear to be declaring fields
+ # in more than one place. We can't be sure (without some extra
+ # bookkeeping) that the rest of the fields will be declared or
+ # have the same positions, so punt.
+ require Carp;
+ Carp::croak ("Reloaded module must declare all fields at once");
+ }
+}
+
+sub inherit { # called by base.pm when $base_fields is nonempty
+ my($derived, $base) = @_;
+ my $base_attr = $attr{$base};
+ my $derived_attr = $attr{$derived} ||= [];
+ # avoid possible typo warnings
+ %{"$base\::FIELDS"} = () unless %{"$base\::FIELDS"};
+ %{"$derived\::FIELDS"} = () unless %{"$derived\::FIELDS"};
+ my $base_fields = \%{"$base\::FIELDS"};
+ my $derived_fields = \%{"$derived\::FIELDS"};
+
+ $derived_attr->[0] = $base_attr ? scalar(@$base_attr) : 1;
+ while (my($k,$v) = each %$base_fields) {
+ my($fno);
+ if ($fno = $derived_fields->{$k} and $fno != $v) {
require Carp;
- Carp::croak("Field name $f already in use");
+ Carp::croak ("Inherited %FIELDS can't override existing %FIELDS");
}
- $fields->{$f} = ++$i;
+ if ($base_attr->[$v] & _PRIVATE) {
+ $derived_attr->[$v] = undef;
+ } else {
+ $derived_attr->[$v] = $base_attr->[$v];
+ $derived_fields->{$k} = $v;
+ }
+ }
+}
+
+sub _dump # sometimes useful for debugging
+{
+ for my $pkg (sort keys %attr) {
+ print "\n$pkg";
+ if (@{"$pkg\::ISA"}) {
+ print " (", join(", ", @{"$pkg\::ISA"}), ")";
+ }
+ print "\n";
+ my $fields = \%{"$pkg\::FIELDS"};
+ for my $f (sort {$fields->{$a} <=> $fields->{$b}} keys %$fields) {
+ my $no = $fields->{$f};
+ print " $no: $f";
+ my $fattr = $attr{$pkg}[$no];
+ if (defined $fattr) {
+ my @a;
+ push(@a, "public") if $fattr & _PUBLIC;
+ push(@a, "private") if $fattr & _PRIVATE;
+ push(@a, "inherited") if $no < $attr{$pkg}[0];
+ print "\t(", join(", ", @a), ")";
+ }
+ print "\n";
+ }
+ }
+}
+
+sub new {
+ my $class = shift;
+ $class = ref $class if ref $class;
+ return bless [\%{$class . "::FIELDS"}], $class;
+}
+
+sub phash {
+ my $h;
+ my $v;
+ if (@_) {
+ if (ref $_[0] eq 'ARRAY') {
+ my $a = shift;
+ @$h{@$a} = 1 .. @$a;
+ if (@_) {
+ $v = shift;
+ unless (! @_ and ref $v eq 'ARRAY') {
+ require Carp;
+ Carp::croak ("Expected at most two array refs\n");
+ }
+ }
+ }
+ else {
+ if (@_ % 2) {
+ require Carp;
+ Carp::croak ("Odd number of elements initializing pseudo-hash\n");
+ }
+ my $i = 0;
+ @$h{grep ++$i % 2, @_} = 1 .. @_ / 2;
+ $i = 0;
+ $v = [grep $i++ % 2, @_];
+ }
+ }
+ else {
+ $h = {};
+ $v = [];
}
- $fields->{__MAX__} = $i;
+ [ $h, @$v ];
}
1;
https://perl5.git.perl.org / perl5.git / blobdiff