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
