On Tue, Sep 19, 2017 at 10:48 AM, Stefan Behnel <stefan...@behnel.de> wrote: > Hi devs, > > this is really bad: > > https://github.com/cython/cython/pull/1873 > > The problem is that cdef functions with fused types are expanded > arbitrarily on use, and their Entries removed and re-appended to the list > of cdef function entries. But that list also defines the order of the > entries in the vtable! > > Currently, when a method with fused types is defined in a .pxd file, it is > the implementation order in the .pyx (!) file that determines the order in > the vtable. Even worse, for modules that cimport from that .pxd file, it is > the order in which these methods are *called* that determines the > corresponding vtable on the other side, as the entries are expanded at > first use, i.e. at their first occurrence in the code, and appended to the > current list of cdef functions at this (arbitrary) point. > > What this means is that there is no way to safely infer the vtable order of > an extension type with fused methods from a .pxd file. > > Now, the correct way to handle this would have been to *replace* the > original fused entry with the expanded list of specialised entries. But > it's too late for that now. All existing modules out there would need to > get recompiled if we changed their vtable order, at least if they use fused > any types methods anywhere in their hierarchy. > > However, I think we can assume code that uses a different method order in > the .pxd and .pyx files to be broken already, so a way out of this misery > would be to make the .pxd order the one and only source, with the twist > that we must keep the "delete and re-append" algorithm to keep the order > that existing translated modules are using. > > Thus the proposal: > > - we switch to a scheme now that is only defined by the first declaration > order, i.e. the order in the .pxd file if there is one. > > - we make sure all fused methods are expanded in that same order, but > continue to follow all non-fused methods in the vtable. > > - we break all code now that uses a different order of fused methods in > their pyx and pxd files > > Thoughts?
+1. We should let the .pxd file, as it is declared, be the source of truth. Code that doesn't already follow this is and does cross-module fused-cdef function calls is already broken. _______________________________________________ cython-devel mailing list cython-devel@python.org https://mail.python.org/mailman/listinfo/cython-devel
