Issue ALLOCATE-INSTANCE Writeup

Issue:         ALLOCATE-INSTANCE


References:    88-002R p.1-41

               89-003 p.3-35


Related issues: LOAD-OBJECTS


Category:      ADDITION


Edit history:  30-Apr-90, Version 1 by Moon


Problem description:


  The function page for the generic function ALLOCATE-INSTANCE was

  accidentally omitted from 88-002R.


Proposal (ALLOCATE-INSTANCE:ADD):


  Add a generic function ALLOCATE-INSTANCE that takes one required

  argument, a class, plus initialization arguments, and returns one value,

  a freshly created instance of the given class.  The class argument must

  be an actual class, not a class name, and must not be a built-in class.


  The object returned by ALLOCATE-INSTANCE is "uninitialized"; when the

  class is a standard class, this means the slots are unbound; when the

  class is a structure class, this means the slots' values are unspecified.


  Common Lisp does not specify how to add methods to ALLOCATE-INSTANCE;

  this capability might be added by the Metaobject Protocol.


  This is Symbolics issue #32 and Loosemore's issue #6 of 27 Feb 90.


Examples:


  (DEFCLASS MYCLASS () (A B C))

  (ALLOCATE-INSTANCE (FIND-CLASS 'MYCLASS))

  (SLOT-BOUNDP * 'B) => NIL


Rationale:


  Some of the authors of 88-002R say the omission of ALLOCATE-INSTANCE was

  simply a mistake.  Note that LOAD-OBJECTS:MAKE-LOAD-FORM assumes the

  existence of ALLOCATE-INSTANCE and that user-written MAKE-LOAD-FORM

  methods that return two values will typically use ALLOCATE-INSTANCE in

  the first value.


Current practice:


  Symbolics Genera 8.0 does not provide ALLOCATE-INSTANCE (although

  it does exist in an internal package).  Lucid 4.0.0 Beta-1 provides

  ALLOCATE-INSTANCE.


Cost to Implementors:


  Any CLOS implementation needs ALLOCATE-INSTANCE or something like it

  internally, so implementing this proposal is largely a matter of

  exporting the symbol from the COMMON-LISP package and documenting it.


Cost to Users:


  None.


Cost of non-adoption:


  MAKE-LOAD-FORM would be considerably less useful.


Performance impact:


  None other than the impact of adding a symbol to the COMMON-LISP package.


Benefits:


  Missing piece of CLOS provided.


Esthetics:


  Neutral.


Discussion:


  None.