On Tue, 2014-01-28 at 16:11 +0100, Stelian Ionescu wrote: > On Tue, 2014-01-28 at 15:33 +0100, Felix Filozov wrote: > > Hi Luís, > > I am hoping to resurrect this thread. Did you by any chance take a > > look at the pull request I made a few months ago relating to this > > feature? > > I strongly object to anything that slows down the common call path, > which is the case here because capture-errno is always called when not > using libffi. > > In addition, IMO this is a hairy-enough case that we should ask the > implementors to add this feature and not do it ourselves. > > As for the interface, the simplest thing might be to add it as last > value - not second because custom foreign types can return multiple > values, e.g. string+ptr - but that will turn out to be slow because I > don't think our current type system knows about arity of custom types > and marshalling unknown numbers of multiple values will cons.
For example
(cffi:defcfun foo :string+ptr (a :int))
on SBCL expands to
(DEFUN FOO (A)
(LET ((#:G1087 A))
(CFFI:TRANSLATE-FROM-FOREIGN
(CFFI-SYS:%FOREIGN-FUNCALL "foo" (:INT #:G1087 :POINTER)
:CONVENTION :CDECL :LIBRARY :DEFAULT)
#<CFFI::FOREIGN-STRING+PTR-TYPE :UTF-8>)))
Since translate-from-foreign is in a tail position we currently don't
care about the number of values it returns, but with errno and knowledge
of multiple values we must make it expand to this:
(defun foo (a)
(let ((#:g1087 a))
(multiple-value-bind (ret errno)
(cffi-sys:%foreign-funcall "foo" (:int #:g1087 :pointer)
:convention :cdecl :library :default)
(multiple-value-bind (val0 val1)
(cffi:translate-from-foreign
ptr #<cffi::foreign-string+ptr-type :utf-8>)))
(values val0 val1 errno)))
--
Stelian Ionescu a.k.a. fe[nl]ix
Quidquid latine dictum sit, altum videtur.
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