> Is there a reason the C++ <> syntax for templates was rejected? > > Brian
I can't seem to find the thread now, so this is from memory. There's the points already mentioned (quoted below); I consider it extremely valuable myself that templates written in Cython are potentially exportable to Python using the same syntax. Also it can be parsed more cleanly. E.g. a<b>(c) Is that two comparisons or calling the constructor of a template? No way to know until you check the type of a and c, meaning the syntax is ambiguous until you check that. (In Python this kind of thing is a showstopper for a new syntax; Guido argues that a simple parser means a language that's also simple to parse by humans). (Even C++ struggles with this kind of thing; requiring you to write "a<b<c> >", i.e. the extra, ugly space to avoid writing a right-shift operator.) In Cython we're not so picky about things like this and there are ways of resolving ambiguous syntax later in the stage; but it does mean that if Python gets generic types (which isn't entirely impossible), <> is out of the question, while we could hope for Python using [] (Guido already used it in mock demonstration syntax for the purpose). > On Thu, May 21, 2009 at 11:16 AM, Dag Sverre > Seljebotn<[email protected]> wrote: >> A decision is needed here within a few weeks; it would be great if any >> core developers who don't care could respond to vote 0. >> >> The decision was made to use [] for templates. To reiterate the main >> arguments: >> >> - It leaves the way open for exporting pre-instantiated templates to >> Python in a /very/ natural fashion. >> >> - Templates are a bit like a collection of types anyway. >> >> >> However this creates some syntax issues: >> >> A) Currently >> >> cdef object[int] arr = ... >> >> can be used for PEP 3118 access on a generic object. While not a >> technical problem (object will never become a template), it looks a bit >> odd when introducing with a template feature. >> >> B) How would a templated buffer type look like? MyType[int][float]? >> >> Proposal: >> >> The object[int] syntax is removed (are anyone using it?). This is >> basically done by making any cdef class with the >> __cythonbufferdefaults__ magic attribute become a "buffer template". >> Such cdef classes cannot be templates. Any other class cannot be used as >> a buffer-supporting object. >> >> This removes functionality (much numeric code could care less about >> whether the underlying object is an ndarray). As a substitute, the main >> idea in http://wiki.cython.org/enhancements/buffersyntax is accepted, >> which is to use >> >> cdef int[:] arr = ... >> >> for generic access, without any object access (this means that for now >> only indexing and getting the shape is allowed at all.) >> >> I've been wondering a lot about whether this is the right way, and it >> still seems so, even if it means that there will be (and likely continue >> to be) two different ways of accessing a buffer; one through an explicit >> "buffer type" and one through an "automatic template". >> >> -- >> Dag Sverre >> _______________________________________________ >> Cython-dev mailing list >> [email protected] >> http://codespeak.net/mailman/listinfo/cython-dev >> > _______________________________________________ > Cython-dev mailing list > [email protected] > http://codespeak.net/mailman/listinfo/cython-dev > _______________________________________________ Cython-dev mailing list [email protected] http://codespeak.net/mailman/listinfo/cython-dev
