On 25/03/2021 18.39, Antoine Pitrou wrote:
> On Thu, 25 Mar 2021 20:22:55 +0300
> Ivan Pozdeev via Python-Dev <[email protected]> wrote:
>> On 24.03.2021 19:58, Antoine Pitrou wrote:
>>> On Wed, 24 Mar 2021 19:45:49 +0300
>>> Ivan Pozdeev via Python-Dev <[email protected]> wrote:
>>>> How does C++ fare in binary compatibility? Last time I checked it out
>>>> (about 10 years ago), there was completely none, every compiler's ABI
>>>> was a black box without any guarantees whatsoever.
>>>> For any software that's going to dynamically link and exchange binary
>>>> types with other independently produced software, that's a deal breaker.
>>> That depends if you use C++ internally or expose C++ bits in the public
>>> API.
>>> If you only use C++ internally, binary compatibility is presumably less
>>> of an issue.
>>
>> Python produces and accepts its internal types in API calls and allows
>> extension modules to derive from them -- so it cannot "only use C++
>> internally" if those are going to become C++ types. (And if not, the point
>> of using C++ is unclear.)
>
> You can use C++ without exposing C++ types in the API. For example,
> C++ templates could improve the maintainability of the generic
> "stringlib" routines that are currently based on C macros. Another
> example is using RAII in function bodies to help cleanup owned
> references.
C has ways to handle cleanup and ownership better -- at least some
compilers do. For example gcc has
__attribute__(cleanup(cleanup_function)) for automatic cleanup on scope
boundaries. If I recall correctly it works something like this:
void
Py_auto_decref(PyObject **o)
{
if (!o || !*o)
return;
Py_DECREF(*o);
*o = NULL;
}
PyObject *
func(PyObject self)
{
PyObject *spam __attribute__((cleanup(Py_auto_decref)));
...
Py_RETURN_NONE;
// spam gets automatically decrefed
}
It's too bad that the feature is not universally available in C99.
Christian
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