Re: lattice of kernel classes

[David A. Moon <Moon@STONY-BROOK.SCRC.Symbolics.COM>]

    Date: 11 Apr 88 13:15 PDT
    From: Danny Bobrow <Bobrow.pa@Xerox.COM>

    The reason for making T be a built-in-class is to ensure that 
    a) no instances of T can be made
    b) No direct subclasses of T can be made (without significant effort)
    I think we need some way to ensure this.  Either we have to make T an exception
    to the rule in Chapter 1, or put this information in more directly in Chpater 3.

What's wrong with (b)?

For (a), if you specifically want an error to be signalled if someone
makes an instance of the class named T, give it a make-instance method
that signals that error.  I don't like errors that get detected by
fortunate coincidences, because that tends to result in error messages
that mere mortals can't understand.