Hi,
ticket 654 describes a code generation problem where the arguments to a
cdef function are not being evaluated in the order they are written down in
the code.
http://trac.cython.org/cython_trac/ticket/654
This introduces problems when the arguments have side effects or are not
simple, e.g. they are function calls themselves or are taken from object
attributes or live in a closure. For example,
f(g(a), a.x, h(a))
will produce different results depending on the evaluation order if g or h
change the value of a.x.
However, apparently, the order of evaluation is only guaranteed by Python,
not by C. Now, the question is: what are the right semantics for Cython
here: follow Python or C?
Personally, I think it would be nice to keep up Python's semantics, but
when I implemented this I broke quite some code in Sage (you may have
noticed that the sage-build project in Hudson has been red for a while).
There are things in C and especially in C++ that cannot be easily copied
into a temporary variable in order to make sure they are evaluated before
the following arguments. This is not a problem for Python function calls
where all arguments end up being copied (and often converted) anyway. It is
a problem for C function calls, though.
What do you think about this?
Stefan
_______________________________________________
cython-devel mailing list
cython-devel@python.org
http://mail.python.org/mailman/listinfo/cython-devel
