package base; use strict 'vars'; use vars qw($VERSION); $VERSION = '2.15'; $VERSION = eval $VERSION; # constant.pm is slow sub SUCCESS () { 1 } sub PUBLIC () { 2**0 } sub PRIVATE () { 2**1 } sub INHERITED () { 2**2 } sub PROTECTED () { 2**3 } my $Fattr = \%fields::attr; sub has_fields { my($base) = shift; my $fglob = ${"$base\::"}{FIELDS}; return( ($fglob && 'GLOB' eq ref($fglob) && *$fglob{HASH}) ? 1 : 0 ); } sub has_version { my($base) = shift; my $vglob = ${$base.'::'}{VERSION}; return( ($vglob && *$vglob{SCALAR}) ? 1 : 0 ); } sub has_attr { my($proto) = shift; my($class) = ref $proto || $proto; return exists $Fattr->{$class}; } sub get_attr { $Fattr->{$_[0]} = [1] unless $Fattr->{$_[0]}; return $Fattr->{$_[0]}; } if ($] < 5.009) { *get_fields = sub { # Shut up a possible typo warning. () = \%{$_[0].'::FIELDS'}; my $f = \%{$_[0].'::FIELDS'}; # should be centralized in fields? perhaps # fields::mk_FIELDS_be_OK. Peh. As long as %{ $package . '::FIELDS' } # is used here anyway, it doesn't matter. bless $f, 'pseudohash' if (ref($f) ne 'pseudohash'); return $f; } } else { *get_fields = sub { # Shut up a possible typo warning. () = \%{$_[0].'::FIELDS'}; return \%{$_[0].'::FIELDS'}; } } sub import { my $class = shift; return SUCCESS unless @_; # List of base classes from which we will inherit %FIELDS. my $fields_base; my $inheritor = caller(0); my @isa_classes; my @bases; foreach my $base (@_) { if ( $inheritor eq $base ) { warn "Class '$inheritor' tried to inherit from itself\n"; } next if grep $_->isa($base), ($inheritor, @bases); if (has_version($base)) { ${$base.'::VERSION'} = '-1, set by base.pm' unless defined ${$base.'::VERSION'}; } else { my $sigdie; { local $SIG{__DIE__}; eval "require $base"; # Only ignore "Can't locate" errors from our eval require. # Other fatal errors (syntax etc) must be reported. die if $@ && $@ !~ /^Can't locate .*? at \(eval /; unless (%{"$base\::"}) { require Carp; local $" = " "; Carp::croak(<[0] = @$battr; if( keys %$dfields ) { warn <<"END"; $derived is inheriting from $base but already has its own fields! This will cause problems. Be sure you use base BEFORE declaring fields. END } # Iterate through the base's fields adding all the non-private # ones to the derived class. Hang on to the original attribute # (Public, Private, etc...) and add Inherited. # This is all too complicated to do efficiently with add_fields(). while (my($k,$v) = each %$bfields) { my $fno; if ($fno = $dfields->{$k} and $fno != $v) { require Carp; Carp::croak ("Inherited fields can't override existing fields"); } if( $battr->[$v] & PRIVATE ) { $dattr->[$v] = PRIVATE | INHERITED; } else { $dattr->[$v] = INHERITED | $battr->[$v]; $dfields->{$k} = $v; } } foreach my $idx (1..$#{$battr}) { next if defined $dattr->[$idx]; $dattr->[$idx] = $battr->[$idx] & INHERITED; } } 1; __END__ =head1 NAME base - Establish an ISA relationship with base classes at compile time =head1 SYNOPSIS package Baz; use base qw(Foo Bar); =head1 DESCRIPTION Unless you are using the C pragma, consider this module discouraged in favor of the lighter-weight C. Allows you to both load one or more modules, while setting up inheritance from those modules at the same time. Roughly similar in effect to package Baz; BEGIN { require Foo; require Bar; push @ISA, qw(Foo Bar); } C employs some heuristics to determine if a module has already been loaded, if it has it doesn't try again. If C tries to C the module it will not die if it cannot find the module's file, but will die on any other error. After all this, should your base class be empty, containing no symbols, it will die. This is useful for inheriting from classes in the same file as yourself, like so: package Foo; sub exclaim { "I can have such a thing?!" } package Bar; use base "Foo"; If $VERSION is not detected even after loading it, will define $VERSION in the base package, setting it to the string C<-1, set by base.pm>. C will also initialize the fields if one of the base classes has it. Multiple inheritance of fields is B supported, if two or more base classes each have inheritable fields the 'base' pragma will croak. See L, L and L for a description of this feature. The base class' C method is B called. =head1 DIAGNOSTICS =over 4 =item Base class package "%s" is empty. base.pm was unable to require the base package, because it was not found in your path. =item Class 'Foo' tried to inherit from itself Attempting to inherit from yourself generates a warning. use Foo; use base 'Foo'; =back =head1 HISTORY This module was introduced with Perl 5.004_04. =head1 CAVEATS Due to the limitations of the implementation, you must use base I you declare any of your own fields. =head1 SEE ALSO L =cut