3 base - Establish IS-A relationship with base class at compile time
12 Roughly similar in effect to
17 push @ISA, qw(Foo Bar);
20 Will also initialize the %FIELDS hash if one of the base classes has
21 it. Multiple inheritance of %FIELDS is not supported. The 'base'
22 pragma will croak if multiple base classes have a %FIELDS hash. See
23 L<fields> for a description of this feature.
25 When strict 'vars' is in scope I<base> also let you assign to @ISA
26 without having to declare @ISA with the 'vars' pragma first.
28 If any of the base classes are not loaded yet, I<base> silently
29 C<require>s them. Whether to C<require> a base class package is
30 determined by the absence of a global $VERSION in the base package.
31 If $VERSION is not detected even after loading it, <base> will
32 define $VERSION in the base package, setting it to the string
33 C<-1, defined by base.pm>.
37 This module was introduced with Perl 5.004_04.
46 use vars qw($VERSION);
54 foreach my $base (@_) {
55 next if $pkg->isa($base);
56 push @{"$pkg\::ISA"}, $base;
57 unless (exists ${"$base\::"}{VERSION}) {
59 # Only ignore "Can't locate" errors from our eval require.
60 # Other fatal errors (syntax etc) must be reported.
61 die if $@ && $@ !~ /^Can't locate .*? at \(eval /;
62 unless (%{"$base\::"}) {
64 Carp::croak("Base class package \"$base\" is empty.\n",
65 "\t(Perhaps you need to 'use' the module ",
66 "which defines that package first.)");
68 ${"$base\::VERSION"} = "-1, set by base.pm"
69 unless exists ${"$base\::"}{VERSION};
72 # A simple test like (defined %{"$base\::FIELDS"}) will
73 # sometimes produce typo warnings because it would create
74 # the hash if it was not present before.
76 if ($fglob = ${"$base\::"}{"FIELDS"} and *$fglob{HASH}) {
79 Carp::croak("Can't multiply inherit %FIELDS");
87 fields::inherit($pkg, $fields_base);