1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
|
================
Design decisions
================
* Generally follow LuaJIT's ffi: http://luajit.org/ext_ffi.html
* Be explicit: almost no automatic conversions. Here is the set
of automatic conversions: the various C integer types are
automatically wrapped and unwrapped to regular applevel integers. The
type ``char`` might correspond to single-character strings instead;
for integer correspondance you would use ``signed char`` or ``unsigned
char``. We might also decide that ``const char *`` automatically maps
to strings; for cases where you don't want that, use ``char *``.
* Integers are not automatically converted when passed as vararg
arguments. You have to use explicitly ``ffi.new("int", 42)`` or
``ffi.new("long", 42)`` to resolve the ambiguity. Floats would be
fine (varargs in C can only accept ``double``, not ``float``), but
there is again ambiguity between characters and strings. Even with
floats the result is a bit strange because passing a float works
but passing an integer not. I would fix this once and for all by
saying that varargs must *always* be a cdata (from ``ffi.new()``).
The possibly acceptable exception would be None (for ``NULL``).
* The internal class ``blob`` is used for raw-malloced data. You only
get a class that has internally a ``blob`` instance (or maybe is a
subclass of ``blob``) by calling ``ffi.new(struct-or-array-type)``.
The other cases, namely the cases where the type is a pointer or a
primitive, don't need a blob because it's not possible to take their
raw address.
* It would be possible to add a debug mode: when we cast ``struct foo``
to ``struct foo *`` or store it in some other struct, then we would
additionally record a weakref to the original ``struct foo`` blob.
If later we try to access the ``struct foo *`` but the weakref shows
that the blob was freed, we complain. This is a difference with
ctypes, which in these cases would store a strong reference and
keep the blob alive. "Explicit is better than implicit", so we ask
the user to keep a reference to the original blob alive as long as
it may be used (instead of doing the right things in 90% of the cases
but still crashing in the remaining 10%).
* LuaJIT uses ``struct foo &`` for a number of things, like for ``p[0]``
if ``p`` is a ``struct foo *``. I suppose it's not a bad idea at least
to have internally such types, even if you can't specify them through
pycparser. Basically ``struct foo &`` is a type that doesn't own a
blob, whereas ``struct foo`` is the type that does.
* LuaJIT uses ``int[?]`` which pycparser doesn't accept. I propose
instead to use ``int[]`` for the same purpose (its use is anyway quite
close to the C standard's use of ``int[]``).
|
