#| -*-Scheme-*-

Copyright (C) 1986, 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994,
    1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005,
    2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016,
    2017, 2018, 2019 Massachusetts Institute of Technology

This file is part of MIT/GNU Scheme.

MIT/GNU Scheme is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or (at
your option) any later version.

MIT/GNU Scheme is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
General Public License for more details.

You should have received a copy of the GNU General Public License
along with MIT/GNU Scheme; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301,
USA.

|#

;;;; Class/Object System

(declare (usual-integrations))

;;; ******************************************************************
;;; This software is intended for use in the Edwin window system only.
;;; Don't think about using it for anything else, since it is not, and
;;; likely will not ever, be supported as a part of the Scheme system.
;;; ******************************************************************

(define-structure (class (constructor %make-class))
  (name false read-only true)
  (superclass false read-only true)
  object-size
  instance-transforms
  (methods false read-only true))

(define (class-method class name)
  (class-methods/ref (class-methods class) name))

(define (class-methods/ref methods name)
  (or (method-lookup methods name)
      (error "Unknown method:" name)))

(define (method-lookup methods name)
  (let loop ((methods methods))
    (and methods
	 (let ((entry (assq name (car methods))))
	   (if entry
	       (cdr entry)
	       (loop (cdr methods)))))))

(define (class-method-define class name method)
  (let ((methods (class-methods class)))
    (let ((entry (assq name (car methods))))
      (if entry
	  (set-cdr! entry method)
	  (set-car! methods (cons (cons name method) (car methods))))))
  name)

(define-integrable (usual-method class name)
  (class-method (class-superclass class) name))

(define (subclass? class class*)
  (or (eq? class class*)
      (let loop ((class (class-superclass class)))
	(and class
	     (or (eq? class class*)
		 (loop (class-superclass class)))))))

(define (make-object class)
  (if (not (class? class))
      (error:wrong-type-argument class "class" 'MAKE-OBJECT))
  (let ((object (make-vector (class-object-size class) false)))
    (vector-set! object 0 class)
    object))

(define (object? object)
  (and (vector? object)
       (not (zero? (vector-length object)))
       (class? (vector-ref object 0))))

(define (object-of-class? class object)
  (and (vector? object)
       (not (zero? (vector-length object)))
       (eq? class (vector-ref object 0))))

(define-integrable (object-class object)
  (vector-ref object 0))

(define-integrable (object-methods object)
  (class-methods (object-class object)))

(define-integrable (object-method object name)
  (class-method (object-class object) name))

(define (send object operation . args)
  (apply (object-method object operation) object args))

(define (send-if-handles object operation . args)
  (let ((method (method-lookup (object-methods object) operation)))
    (and method (apply method object args))))

(define (send-usual class object operation . args)
  (apply (usual-method class operation) object args))