with-pointers vs. with-macptrs

[bill@cambridge.apple.com (Bill St. Clair)]

At  2:54 PM 7/13/93 -0500, Terrance Paul McCartney wrote:
>Does anyone know the difference between "with-pointers" and "with-macptrs"?
>I am developing GWorld intensive software, and some of the examples that I 
>have seen use both of these.  However, "with-macptrs" is not described in
>the manual.  Is one more stable than the other?
>
>- Paul

WITH-MACPTRS & WITH-POINTERS are entirely different.
WITH-MACPTRS is basically the same as LET except that it expects
all of the values to be MACPTRs and arranges for them to all have
dynamic-extent:

? (pprint (macroexpand '(with-macptrs ((x (foo))))))

(LET* ((X (%SETF-MACPTR (%NULL-PTR) (FOO))))
  (DECLARE (DYNAMIC-EXTENT X))
  (DECLARE (TYPE MACPTR X)))
? 

WITH-POINTERS locks and dereferences any values which are HANDLEP
during the execution of its body:

? (pprint (macroexpand '(with-pointers ((x (foo))))))

(LET ((#:G52 (FOO)) #:G51)
  (DECLARE (DYNAMIC-EXTENT #:G52))
  (UNWIND-PROTECT
      (WITH-MACPTRS (X) (SETQ #:G51 (CCL::%THING-POINTER #:G52 0 X)) (PROGN))
    (WHEN #:G51 (REQUIRE-TRAP TRAPS::_HUNLOCK #:G51))))


; %thing-pointer is an internal MCL function.
(defun %thing-pointer (pointer offset locked-ptr)
  (if (macptrp pointer)
    (let ((unlock-ptr nil))
      (if (handlep pointer)
        (progn
          (unless (handle-locked-p pointer)
            (setq unlock-ptr pointer)
            (#_HLock :errchk pointer))
          (%setf-macptr locked-ptr (%get-ptr pointer))
          (%strip-address locked-ptr))
        (%setf-macptr locked-ptr pointer))
      (%incf-ptr locked-ptr offset)
      unlock-ptr)
    (report-bad-arg pointer '(satisfies macptrp))))