Macros in C have a lot of problems, so I think it's best to avoid them whenever possible. In particular:
- The symbols they define don't show up in the debugger, memory profiler, or other tools. - They work at the textual level, so it's easy to get incorrect behaviour if you forget to add extra parenthesis that aren't needed in normal C. - When using them to define an inline "function," they can't always be used all places a function can. In your example: #define _fqtypename(o) (((PyTypeObject*)o)->ob_type->tp_name) _fqtypename(a + b) expands to: (((PyTypeObject*)a + b)->ob_type->tp_name) And by C's precedence rules, the cast applies to "a" *before* "b" is added. If you want an inline function, why not just declare it inline? The use cases discussed on the list recently were to get around the fact that Cython doesn't know all that much about C or C++. Why not just teach it more? No language that learned from C, such as Java and Python, include macros. C++ tries hard to provide language support for all idioms that C needs them for, and there's even some talk of deprecating macros in C++ (IIRC). So, I think the response should be to teach Cython about references, rather than macros. What do people think? Best, Martin Stefan Behnel wrote: > Hi, > > since William brought up this topic lately, I think there are a couple of very > valid cases where you want to define a macro in C and use it as a function in > Cython. This currently means: > > 1) write a macros.h file to hold the macro > 2) add a 'cdef extern from "macros.h"' to your favourite .pxd file to define > your macros in Cython > > So this requires you to keep track of two files for things that may just be a > couple of lines in C. > > I think this is so common that it would help if you could write inline C code > in a .pxd file and have it written into your generated C file automatically. I > could imagine a syntax like this: > > # macros.pxd > MACROS = """ > #define _isString(obj) (PyString_CheckExact(obj) || \ > PyUnicode_CheckExact(obj) || \ > PyObject_TypeCheck(obj, &PyBaseString_Type)) > > #define _fqtypename(o) (((PyTypeObject*)o)->ob_type->tp_name) > """ > > cdef inline from MACROS: > cdef int _isString(object obj) > cdef char* _fqtypename(object t) > > Instead of an '#include "macros.h"', this would write the string given by > MACROS verbatimly into the C file, directly behind the #include section. It > could also keep track of the strings in a set to make sure they are only > written out once, even when cimported redundantly at various places. > > Any comments on this? > > Stefan > > > _______________________________________________ > 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
