direct-instance declarations

[Mark Nahabedian <naha@RIVERSIDE.SCRC.Symbolics.COM>]

    Date: Fri, 6 Nov 1992 08:47 EST
    From: Jonathan Bachrach <Jonathan.Bachrach@ircam.fr>

    Sealed-classes provide a mechanism for reducing dispatching, but
    unfortunately the current mechanism is limited in annoying ways.
    First, dispatching is performed at compile-time for only
    sealed-classes at the leaves of the class heterarchy.  This prevents
    creating efficient instantiable classes with subclasses.  Secondly,
    after sealing a class it is forbidden to create a new subclass for
    that class.  

I don't see this as a significant restriction.  I would see myself not
sealing a class untill I was ready to build a "shipable" executable of
my application.  At that point there is no longer a development
environment and there is no possibility of adding subclasses anyway.  I
don't think it's a big disadvantage to not seal a class until the
development cycle is over.

		 This means, for example, that none of the code for the
    classes in the sealed collection classes can be leverage -- for
    example it is impossible to create a new <table> subclass with a
    slight variation.

    [...]