Re: Proposed revision of "Inheritance of Slots and Slot Options" section

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

    Date: 27 Feb 87 16:20 PST
    From: Danny Bobrow <Bobrow.pa@Xerox.COM>

    In general I agree with Moon that slot inheritance is simple and like
    his rewording.  A few minor glitches:

	If the :allocation slot option is omitted or specifies a local
	slot, then each instance of C stores its own value for the slot.  

    This needs to be specific about local being either :instance or :dynamic
    (or perhaps it should have that earlier).

An earlier item on the errata sheet was to add :dynamic where it had been
left out.  But I agree that it's better to mention the specific keywords
here too, so I added that to the revised errata sheet I am about to mail
out.

    Secondly, the type constraint is presented very strongly.  The intent of
    having it (I pushed it in) was to allow compatibility with current
    defstruct.  Current defstruct does not specify that a slot MUST meet its
    type constraint.  Consequently, I would suggest that the rule specify:

    "The :type of a slot need not be specified.  If it is, the
    interpretation is that the value of the slot should be of type (and T1
    T2 T3...), where T1 , ... Tn are all the type specifiers provided in any
    slot specifcation.  Implementations need not check for values, but those
    that do should use the interpretation, and hence may optimize for those
    values."

In 87-002 it seems we forgot to say anywhere what :type really means.
The errata sheet for chapter 2 says something that I think is equivalent
to what you just said.