Robert Bradshaw schrieb am 19.09.2017 um 22:55: > On Tue, Sep 19, 2017 at 10:48 AM, Stefan Behnel wrote: >> 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.
This should fix it: https://github.com/cython/cython/commit/fcc3461e0077c86e30cc81a2fd78bce60f1be007 There were also other problems that I could fix along the way with respect to inheritance from types with fused cdef methods, so I can hope that we're really fixing a rare case in practice. At least, it took more than 5 years after implementing fused types (in April 2012) to discover this bug, so it can't be the most widely used Cython feature out there... Stefan _______________________________________________ cython-devel mailing list cython-devel@python.org https://mail.python.org/mailman/listinfo/cython-devel
