Re: [Sbcl-devel] CFFI buglet (Was: caught ERROR: Malformed LET bindings)

[Vitaly M. <v.m...@gm...>]

At Wed, 5 Aug 2009 19:07:49 +0300, Nikodemus Siivola wrote:

> Yes, it's a but -- but I believe a bug in CFFI. Explanation follows.
> (Example demonstrating an alternative way to trigger comes right at
> the end.)
> 
> In the expansion, this is the problematic form:
> 
> (DEFMETHOD (SETF MY-STRUCT-FOO) ((INST MY-STRUCT) NEW)
>   (SETF (CFFI:FOREIGN-SLOT-VALUE (SLOT-VALUE INST 'RAW) 'MY-STRUCT
>                                  'FOO)
>         NEW))
> 
> first off, this probably does not do what you think it does: the new value is
> the first argument, not the last.

Yes, it is correct in my code, I did a typo in this smaller piece of code.

> Notice how the same error can be provoked without the PCL code walker:
> 
> (defun my-bad (x z)
>   (setf (cffi:foreign-slot-value (let ((y (x-y x)))
>                                    (y-foreign y))
>                                  'my-struct
>                                  'foo)
>         z))
> 
> Unless the contract of (SETF FOREIGN-SLOT-VALUE) is that the first
> (second) argument
> must be a settable place itself, the compiler-macro is broken.

Ok, thanks for explanation.
-- 
wbr, Vitaly