Given that two respected Perl gurus both thought that this
would break, here is a working test with three modules.
Foo and Bar are abstract. Baz must implement their abstract
methods.
Here is Foo.pm:
package Foo;
use Carp;
# Import method that checks existence of abstract methods in subclasse
+s.
sub import {
my $pkg = shift;
return if $pkg eq __PACKAGE__;
foreach my $meth ( qw(foo) ) {
$pkg->can($meth) or croak("Class $pkg does not define method $meth
+");
}
$pkg->SUPER::import(@_);
}
1;
Here is Bar.pm:
package Bar;
use Carp;
use Foo;
@ISA = qw(Foo);
# Import method that checks existence of abstract methods in subclasse
+s.
sub import {
my $pkg = shift;
return if $pkg eq __PACKAGE__;
foreach my $meth ( qw(bar) ) {
$pkg->can($meth) or croak("Class $pkg does not define method $meth
+");
}
$pkg->SUPER::import(@_);
}
1;
Here is Baz.pm:
package Baz;
use Bar;
@ISA = qw(Bar);
sub foo {print "This is method foo\n";}
sub bar {print "This is method bar\n";}
1;
And then here is the test script:
use Baz;
If you comment out either sub in Baz.pm, the program will
die immediately.