Next time I'll limit the bonus points to Monks or below :)

The use of __PACKAGE__ was what I was looking for. I was thinking along the lines of

    package AbstractFoo;
    ...
    sub new {
        my $package = shift;
        die __PACKAGE __ . " is an abstract class"
            if $package eq __PACKAGE__;
        bless { @_ }, $package;
    }
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merlyn and I had a back and forth in the CB about the difference between his solution and mine. I noted that his would fail if nobody in AbstractFoo's superclass chain implemented new. merlyn agreed, saying (and here I'll ask him to correct me if I get the details wrong) that this was correct behavior, given that there's no generic way to implement new. I granted that point, but cited the Smalltalk image as evidence that there were common patterns. That, in essense, is where we left the discussion.