Just that I'd limit the counter variable to the routines that need it; so it seems that the variable doesn't exist in parts of your class that are outside the scope created by the outermost brackets below. 
{
    my $count;  # Number of class instances that exist.

    sub BUILD {
        ++$count;
        #
    }

    sub DEMOLISH {
        --$count;
        #
    }
}

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Be well,
rir

In reply to Re^3: Garbage collected class attributes with inside out classes. by rir
in thread Garbage collected class attributes with inside out classes. by kyle

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