On Mon, Aug 22, 2016 at 7:44 AM, Kevin Thornton <krtho...@uci.edu> wrote: > I actually just realized another nagging issue with C++/Cython: member > typedefs are not supported: > > cdef vector[T]: > ctypedef size_t size_type > > These "scoped" typedefs are very widely-used. We can live without it, and > we have been, but while we're making a list.. :)
Yes, that's a good one. Worth an issue :). > On Sat, Aug 20, 2016 at 11:15 PM Robert Bradshaw <rober...@gmail.com> wrote: >> >> On Fri, Aug 19, 2016 at 9:34 AM, Kevin Thornton <krtho...@uci.edu> wrote: >> > Hi Robert, >> > >> > Related to this point, I think there are three important features that >> > Cython would benefit from, as far as C++11 and newer are concerned. In >> > order of what I'm guessing to be increased complexity are: >> > >> > 1. Non-type template parameters. >> >> This is actually probably the hardest :). There is a PR that's stalled >> out, probably needs some attention by both the author and us; it'd be >> great to get this in. >> >> > 2. "rvalue" references for standalone functions and class member >> > functions: >> > >> > void foo[T]( T && t ) >> >> From a callers perspective, one can just declare an extern foo as >> foo(T) in Cython, it doesn't care if the actual call is made by value >> or by reference--the calling code is exactly the same. >> >> Actually implementing it for Cython-defined functions (as the callee) >> would require additional support, but would probably be pretty easy >> (implement a new type, with parsing, which generally behaves the same >> as a reference or value from Python's perspective--the actual heavy >> lifting happens in the C compiler). >> >> Want to file an issue on github for this? >> >> > 3. Variadic templates (member and non-member). More generally, >> > "parameter >> > packs": >> > >> > http://en.cppreference.com/w/cpp/language/parameter_pack >> >> This'd be interesting (especially as to how it relates to changing the >> arity of functions for concrete instantiations). There's also a >> question of syntax. Maybe >> >> void foo[A, int N, ... Types](A a, Types t): >> ... >> >> It'd likely require #1, e.g. to be able to declare things like >> tuple_element::type such that std::tuple.get<N> would be correctly >> typed. Unfortunately seems declaring the (somewhat intuitive) API of >> std::tuple requires being able to declare a fair amount of its >> implementation. >> >> Still likely feasible though, and I think the notion of variadic >> templates is natural enough in a Python setting (which has had >> heterogeneously typed tuples since its inception, though of course not >> statically typed). >> >> > #2 is important for efficiency reasons--it isn't just a convenience >> > feature. >> > Without it, Cython cannot support all the member function of >> > std::vector, >> > etc. The implication is that some expensive operations, like moving a >> > big >> > object into a vector, require extra copies in Cython while a C++ program >> > would just move the object into the new location. >> >> It's interesting to call this an essential feature, given that C++ >> itself didn't have it until recently :). Not that it can't be a big >> win, and libraries will more and more probably be designed assuming >> it. >> >> > #3 seems like the hardest, but would enable std::tuple, std::bind, and >> > other >> > handy things to be used in a .pyx file. >> > >> > Support for "auto" would be nice, but perhaps unrealistic. >> >> Just leave the cdef out and you basically get auto, i.e. >> >> my_var = expr >> >> gives my_var the type of expr. If multiple assignments are made to >> my_var, it attempts to find a suitable union type that can hold all >> assignments. The one exception is for integers, where it infers the >> type to be object iff my_var is used in arithmetic expressions (that >> it can't deduce would not overflow with the finite-sized C integer >> type). >> >> > I know that PRs have been submitted, and since stalled out, on a couple >> > of >> > these features. I've tried to look at the Cython parser myself, but I'm >> > not >> > able to follow it, sadly. >> > >> > Thanks for all your hard work, >> > >> > Kevin >> > >> > On Fri, Aug 19, 2016 at 2:39 AM Robert Bradshaw <rober...@gmail.com> >> > wrote: >> >> >> >> >> >> Though, as you discovered, there are some basic things like non-type >> >> template arguments that we would like to have. If there are other >> >> specific C++ constructs that are commonly used but impossible to >> >> express in Cython it'd be useful to know. >> >> >> >> >> >> _______________________________________________ >> >> cython-devel mailing list >> >> cython-devel@python.org >> >> https://mail.python.org/mailman/listinfo/cython-devel >> > >> > >> > _______________________________________________ >> > cython-devel mailing list >> > cython-devel@python.org >> > https://mail.python.org/mailman/listinfo/cython-devel >> > >> _______________________________________________ >> cython-devel mailing list >> cython-devel@python.org >> https://mail.python.org/mailman/listinfo/cython-devel > > > _______________________________________________ > cython-devel mailing list > cython-devel@python.org > https://mail.python.org/mailman/listinfo/cython-devel > _______________________________________________ cython-devel mailing list cython-devel@python.org https://mail.python.org/mailman/listinfo/cython-devel
