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	---
	tmapping.lisp (2910B)
	---
	1 ;;;; -- Mode: lisp; indent-tabs-mode: nil --
	2 ;;;
	3 ;;; mapping.lisp --- An example for mapping Lisp objects to ints.
	4 ;;;
	5 ;;; Copyright (C) 2007, Luis Oliveira <[email protected]>
	6 ;;;
	7 ;;; Permission is hereby granted, free of charge, to any person
	8 ;;; obtaining a copy of this software and associated documentation
	9 ;;; files (the "Software"), to deal in the Software without
	10 ;;; restriction, including without limitation the rights to use, copy,
	11 ;;; modify, merge, publish, distribute, sublicense, and/or sell copies
	12 ;;; of the Software, and to permit persons to whom the Software is
	13 ;;; furnished to do so, subject to the following conditions:
	14 ;;;
	15 ;;; The above copyright notice and this permission notice shall be
	16 ;;; included in all copies or substantial portions of the Software.
	17 ;;;
	18 ;;; THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
	19 ;;; EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
	20 ;;; MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
	21 ;;; NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
	22 ;;; HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
	23 ;;; WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
	24 ;;; OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
	25 ;;; DEALINGS IN THE SOFTWARE.
	26 ;;;
	27
	28 ;;; This is an example on how to tackle the problem of passing Lisp
	29 ;;; object identifiers to foreign code. It is not a great example,
	30 ;;; but might be useful nevertheless.
	31 ;;;
	32 ;;; Requires trivial-garbage: <http://cliki.net/trivial-garbage>
	33
	34 (defpackage #:cffi-mapping-test
	35 (:use #:common-lisp #:cffi #:trivial-garbage)
	36 (:export #:run))
	37
	38 (in-package #:cffi-mapping-test)
	39
	40 (define-foreign-type lisp-object-type ()
	41 ((weakp :initarg :weakp))
	42 (:actual-type :unsigned-int))
	43
	44 (define-parse-method lisp-object (&key weak-mapping)
	45 (make-instance 'lisp-object-type :weakp weak-mapping))
	46
	47 (defvar regular-hashtable (make-hash-table))
	48 (defvar weak-hashtable (make-weak-hash-table :weakness :value))
	49 (defvar regular-counter 0)
	50 (defvar weak-counter 0)
	51
	52 (defun increment-counter (value)
	53 (mod (1+ value) (expt 2 (* 8 (foreign-type-size :unsigned-int)))))
	54
	55 (define-modify-macro incf-counter () increment-counter)
	56
	57 (defmethod translate-to-foreign (value (type lisp-object-type))
	58 (with-slots (weakp) type
	59 (let ((id (if weakp
	60 (incf-counter weak-counter)
	61 (incf-counter regular-counter)))
	62 (ht (if weakp weak-hashtable regular-hashtable)))
	63 (setf (gethash id ht) value)
	64 id)))
	65
	66 (defmethod translate-from-foreign (int (type lisp-object-type))
	67 (with-slots (weakp) type
	68 (gethash int (if weakp weak-hashtable regular-hashtable))))
	69
	70 ;;;; Silly example.
	71
	72 (defctype weak-mapping (lisp-object :weak-mapping t))
	73
	74 ;;; (run) => #<FUNCTION (LAMBDA (X)) {11AB46F5}>
	75 (defun run ()
	76 (foreign-funcall "abs" weak-mapping (lambda (x) x) weak-mapping))