I'm not sure how to address Ryan's case (what I identified as (1)). I am (effectively) scrapping the changes I have made by redefining defmethod aggregatep ((type foreign-pointer-type)) to give nil, because I found having it T seriously broke GSLL. I acknowledge your points and Ryan's in his last email but I don't understand pointers and aggregates and structures in C and how they should map to CL enough to understand what to do. Any thoughts appreciated (Luis? anyone?).
Liam On Mon, Feb 20, 2012 at 10:38 AM, Martin Simmons <mar...@lispworks.com>wrote: > This looks wrong to me -- a pointer is not an aggregate type. Also, I > think > your test-new-ptr-ref and test-generic-ptr-ref tests are bogus because the > type in mem-aref doesn't match the type of ptr. > > Have you tried it with a struct containing 20 bytes? Testing it with an > array > of two 4 byte structs leads to confusion about the size of a pointer v.s. > the > size of one struct v.s. the size of the array. > > In fact, I don't understand what mem-aref is supposed to do for an > aggregate > type. Making it return a pointer to the first byte of the aggregate is > inconsistent with how it treats other types and IMHO leads to the current > confusion. > > __Martin > > > > >>>>> On Sat, 18 Feb 2012 12:53:17 -0500, Liam Healy said: > > > > The new syntax is as follows. If you want the structure itself, use > > (:struct foo). If you want a pointer to it, use (:pointer (:struct > > foo)). The latter should be identical to the old style bare struct > > specification, except for the annoying deprecation warning, of course. > > > > The issues I can identify, with their resolutions: > > > > 1) Using mem-aref with the (:pointer (:struct ...)) spec gives the wrong > > pointer. > > > > I have fixed an error which should now return the correct pointer for an > > offset of 0. For an offset of 1, it returns the base pointer +8 bytes, > > which is not what the old style gives (+ 4 bytes), but it seems to me > > correct, as I understand the index to refer to the number of whole > > structures. Pull ee90bfd517 and try. > > > > 2) The plist form representing the structure is not desirable. > > > > You can have any CL representation of the structure you like; you need to > > define a method cffi:translate-from-foreign for your type class. You are > > getting the default, a plist translation, because no such method is > > defined. See for example how I translate complex > > numbers< > http://repo.or.cz/w/antik.git/blob/1ee407c69525b84b441f8cf7b48ac590e78bd635:/foreign-array/complex-types.lisp#l50 > >to > > CL complex numbers. You can even return a pointer if you want, but > > this > > probably isn't the specification to use if you want the pointer. > > > > > > On Mon, Feb 13, 2012 at 10:22 AM, Ryan Pavlik < > > > reply+i-1614209-ba246666762196459413560690eb7d3a39c7c7ee-838...@reply.github.com > > > wrote: > > > > > I've pulled the latest and it appears the semantics have changed for > > > mem-aref, but there is still no way to get the old behavior. Here is a > > > complete example, though it doesn't use the test system definitions > because > > > actual foreign calls and definitions aren't really the problem: > > > > > > ``` > > > (asdf:load-system :cffi) > > > > > > (cffi:defcstruct my-struct > > > (x :short) > > > (y :short)) > > > > > > (defun test-old-ref () > > > (declare (notinline cffi:mem-ref cffi:mem-aref)) > > > (cffi:with-foreign-object (ptr '(:struct my-struct) 2) > > > (format t "~&Old-ref style:~%ptr : ~A~%aref: ~A~%" > > > ptr (cffi:mem-aref ptr 'my-struct 1)))) > > > > > > (defun test-new-ref () > > > (cffi:with-foreign-object (ptr '(:struct my-struct) 2) > > > (format t "~&New-ref style:~%ptr : ~A~%aref: ~A~%" > > > ptr > > > (cffi:mem-aref ptr '(:struct my-struct) 1)))) > > > > > > (defun test-new-ptr-ref () > > > (cffi:with-foreign-object (ptr '(:struct my-struct) 2) > > > (format t "~&New-ref with :pointer style:~%ptr : ~A~%aref: ~A~%" > > > ptr > > > (cffi:mem-aref ptr '(:pointer (:struct my-struct)) 1)))) > > > > > > (progn > > > (test-old-ref) > > > (test-new-ref) > > > (test-new-ptr-ref)) > > > ``` > > > > > > The output I get, sans style-warnings about bare structs: > > > > > > ``` > > > Old-ref style: > > > ptr : #.(SB-SYS:INT-SAP #X7FFFEEFCFFF0) > > > aref: #.(SB-SYS:INT-SAP #X7FFFEEFCFFF4) > > > New-ref style: > > > ptr : #.(SB-SYS:INT-SAP #X7FFFEEFCFFF0) > > > aref: (Y 0 X 0) > > > New-ref with :pointer style: > > > ptr : #.(SB-SYS:INT-SAP #X7FFFEEFCFFF0) > > > aref: #.(SB-SYS:INT-SAP #X00000000) > > > ``` > > > > > > Note that in the first example, with the original semantics, if you > > > mem-aref a pointer to an array of `my-struct`, you get a pointer to the > > > array element. In the new style, with `(:struct my-struct)`, you get > the > > > values parsed into a list, which is not particularly useful; it > conses, and > > > you almost certainly have to re-parse a possibly long list for a single > > > element. In the new style with `:pointer`, it appears to dereference > the > > > Nth element in an *array of pointers to my-struct*, which is not at all > > > what we want. > > > > > > The latter differs from the behavior before I updated, which seemed to > > > return a *pointer* to the Nth element in an array-of-pointers. None > of the > > > above are like the old behavior. > > > > > > --- > > > Reply to this email directly or view it on GitHub: > > > https://github.com/cffi/cffi/pull/2#issuecomment-3941718 > > > > > > > _______________________________________________ > cffi-devel mailing list > cffi-devel@common-lisp.net > http://lists.common-lisp.net/cgi-bin/mailman/listinfo/cffi-devel >
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