X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=lib%2Ffields.pm;h=a64469c161f5a45e289ef92f7fbf879e8ffaf648;hb=c9bca74aca217023baf0f921dcffaaa072a83cf3;hp=c2cf1d6a5df5c23a3bbf49a6b82021edc34c6adf;hpb=d516a115cc96334486070e15a6babcd1278d8de9;p=p5sagit%2Fp5-mst-13.2.git diff --git a/lib/fields.pm b/lib/fields.pm index c2cf1d6..a64469c 100644 --- a/lib/fields.pm +++ b/lib/fields.pm @@ -8,34 +8,220 @@ fields - compile-time class fields { 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 $var = Foo->new; $var->{foo} = 42; - # This will generate a compile-time error. + # this will generate an 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 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 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. + +The related C pragma will combine fields from base classes and any +fields declared using the C 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 following functions are supported: + +=over 8 + +=item new + +fields::new() creates and blesses a restricted-hash comprised of the +fields declared using the C 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 $self = shift; + $self = fields::new($self) unless ref $self; + $self->{cat} = 'meow'; # scalar element + @$self{'dog','bird'} = ('bark','tweet'); # slice + return $self; + } + +=item phash + +Pseudo-hashes have been removed from Perl as of 5.10. Consider using +restricted hashes instead. Using fields::phash() will cause an error. + +=back + +=head1 SEE ALSO + +L, + =cut +use 5.006_001; +use strict; +no strict 'refs'; +use warnings::register; +our(%attr, $VERSION); + +$VERSION = "1.02"; + +use Hash::Util qw(lock_keys); + +# 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; - Carp::croak("Field name $f already in use"); + if ($fno < $fattr->[0]) { + warnings::warnif("Hides field '$f' in base class") ; + } else { + Carp::croak("Field name '$f' already in use"); + } } - $fields->{$f} = ++$i; + $fields->{$f} = $next; + $fattr->[$next] = ($f =~ /^_/) ? _PRIVATE : _PUBLIC; + $next += 1; } - $fields->{__MAX__} = $i; + if (@$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 != $v) { + require Carp; + Carp::croak ("Inherited %FIELDS can't override existing %FIELDS"); + } + if ($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; + my $self = bless {}, $class; + lock_keys(%$self, keys %{$class.'::FIELDS'}); + return $self; +} + +sub phash { + die "Pseudo-hashes have been removed from Perl"; } 1;