X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=lib%2Ffields.pm;h=cca778f905d971f26afccd20400db45af4c74c10;hb=a6f787ca70fe8281557cb1a6f45d147f91cb88bb;hp=2727a043e271b8030d71feb5aaee2e8436982906;hpb=f30a114324770080b9e0b2bcfb9c2278f5e0a290;p=p5sagit%2Fp5-mst-13.2.git diff --git a/lib/fields.pm b/lib/fields.pm index 2727a04..cca778f 100644 --- a/lib/fields.pm +++ b/lib/fields.pm @@ -1,83 +1,24 @@ package fields; -=head1 NAME - -fields - compile-time class fields - -=head1 SYNOPSIS - - { - package Foo; - use fields qw(foo bar _private); - } - ... - my Foo $var = new Foo; - $var->{foo} = 42; - - # This will generate a compile-time error. - $var->{zap} = 42; - - { - package Bar; - use base 'Foo'; - use fields 'bar'; # hides Foo->{bar} - use fields qw(baz _private); # not shared with Foo - } - -=head1 DESCRIPTION - -The C pragma enables compile-time verified class fields. It -does so by updating the %FIELDS hash in the calling package. - -If a typed lexical variable holding a reference is used to access a -hash element and the %FIELDS hash of the given type exists, then the -operation is turned into an array access at compile time. The %FIELDS -hash maps from hash element names to the array indices. If the hash -element is not present in the %FIELDS hash, then a compile-time error -is signaled. - -Since the %FIELDS hash is used at compile-time, it must be set up at -compile-time too. This is made easier with the help of the 'fields' -and the 'base' pragma modules. The 'base' pragma will copy fields -from base classes and the 'fields' pragma adds new fields. Field -names that start with an underscore character are made private to a -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. -For untyped access to work you have to make sure that a reference to -the proper %FIELDS hash is assigned to the 0'th element of the array -object (so that the objects can be treated like an pseudo-hash). A -constructor like this does the job: - - sub new - { - my $class = shift; - no strict 'refs'; - my $self = bless [\%{"$class\::FIELDS"}], $class; - $self; - } - - -=head1 SEE ALSO - -L, -L - -=cut - +require 5.005; use strict; no strict 'refs'; +unless( eval q{require warnings::register; warnings::register->import} ) { + *warnings::warnif = sub { + require Carp; + Carp::carp(@_); + } +} use vars qw(%attr $VERSION); -$VERSION = "1.01"; +$VERSION = '2.03'; + +# constant.pm is slow +sub PUBLIC () { 2**0 } +sub PRIVATE () { 2**1 } +sub INHERITED () { 2**2 } +sub PROTECTED () { 2**3 } -# 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 @@ -91,10 +32,15 @@ sub import { my $class = shift; return unless @_; my $package = caller(0); + # avoid possible typo warnings + %{"$package\::FIELDS"} = () unless %{"$package\::FIELDS"}; my $fields = \%{"$package\::FIELDS"}; my $fattr = ($attr{$package} ||= [1]); my $next = @$fattr; + # Quiet pseudo-hash deprecation warning for uses of fields::new. + bless \%{"$package\::FIELDS"}, 'pseudohash'; + if ($next > $fattr->[0] and ($fields->{$_[0]} || 0) >= $fattr->[0]) { @@ -110,13 +56,17 @@ sub import { if ($fno and $fno != $next) { require Carp; if ($fno < $fattr->[0]) { - Carp::carp("Hides field '$f' in base class") if $^W; + if ($] < 5.006001) { + warn("Hides field '$f' in base class") if $^W; + } else { + warnings::warnif("Hides field '$f' in base class") ; + } } else { Carp::croak("Field name '$f' already in use"); } } $fields->{$f} = $next; - $fattr->[$next] = ($f =~ /^_/) ? _PRIVATE : _PUBLIC; + $fattr->[$next] = ($f =~ /^_/) ? PRIVATE : PUBLIC; $next += 1; } if (@$fattr > $next) { @@ -130,53 +80,240 @@ sub import { } } -sub inherit # called by base.pm when $base_fields is nonempty +sub inherit { + require base; + goto &base::inherit_fields; +} + +sub _dump # sometimes useful for debugging { - my($derived, $base) = @_; - my $base_attr = $attr{$base}; - my $derived_attr = $attr{$derived} ||= []; - 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"); + for my $pkg (sort keys %attr) { + print "\n$pkg"; + if (@{"$pkg\::ISA"}) { + print " (", join(", ", @{"$pkg\::ISA"}), ")"; } - if ($base_attr->[$v] & _PRIVATE) { - $derived_attr->[$v] = undef; - } else { - $derived_attr->[$v] = $base_attr->[$v]; - $derived_fields->{$k} = $v; + 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 $fattr & INHERITED; + print "\t(", join(", ", @a), ")"; + } + print "\n"; } - } + } } -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"; - } - } +if ($] < 5.009) { + *new = sub { + my $class = shift; + $class = ref $class if ref $class; + return bless [\%{$class . "::FIELDS"}], $class; + } +} else { + *new = sub { + my $class = shift; + $class = ref $class if ref $class; + require Hash::Util; + my $self = bless {}, $class; + + # The lock_keys() prototype won't work since we require Hash::Util :( + &Hash::Util::lock_keys(\%$self, keys %{$class.'::FIELDS'}); + return $self; + } +} + +sub phash { + die "Pseudo-hashes have been removed from Perl" if $] >= 5.009; + 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 = []; + } + [ $h, @$v ]; + } 1; + +__END__ + +=head1 NAME + +fields - compile-time class fields + +=head1 SYNOPSIS + + { + package Foo; + 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 $var = Foo->new; + $var->{foo} = 42; + + # 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. + +B + +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 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. + +B + +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 4 + +=item new + +B< perl before 5.9.0: > fields::new() creates and blesses a +pseudo-hash comprised of the fields declared using the C +pragma into the specified class. + +B< perl 5.9.0 and higher: > fields::new() creates and blesses a +restricted-hash comprised of the fields declared using the C +pragma into the specified class. + +This function is usable with or without pseudo-hashes. It is the +recommended way to construct a fields-based object. + +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 + +B< before perl 5.9.0: > + +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); + +B< perl 5.9.0 and higher: > + +Pseudo-hashes have been removed from Perl as of 5.10. Consider using +restricted hashes or fields::new() instead. Using fields::phash() +will cause an error. + +=back + +=head1 SEE ALSO + +L + +=cut