If B inherits A, and B::foo isn't defined, but A::foo is, calling B::foo will fail. There's no such sub.

If you want Perl to act in an OO way, you should make a method call, not a sub call. Use B->foo, and A::foo will be called.

If you can't or won't, you're out of luck.

use strict;
use warnings;

$| = 1;

sub A::foo {print "This is A::foo\n"}
@B::ISA = qw /A/;

print "Calling B->foo(): "; B->foo();
print "Calling B::foo(): "; B::foo();

__END__
Calling B->foo(): This is A::foo
Calling B::foo(): Undefined subroutine &B::foo called at ...
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