[PyQt] Empty and template classes

[Shaheed Haque]

Hi Phil,

On 10 April 2016 at 16:40, Phil Thompson <phil at riverbankcomputing.com> wrote:
> On 10 Apr 2016, at 2:53 pm, Shaheed Haque <srhaque at theiet.org> wrote:
>>
>> Hi Phil,
>>
>> On 10 April 2016 at 13:32, Phil Thompson <phil at riverbankcomputing.com> wrote:
>>> On 10 Apr 2016, at 1:21 pm, Shaheed Haque <srhaque at theiet.org> wrote:
>>>>
>>>> Hi,
>>>>
>>>> One enhancement request, and a question. First, SIP 4.16.9 does not
>>>> like empty classes like this:
>>>>
>>>> class KUserOrGroupId
>>>> {
>>>> };
>>>>
>>>> The above results in a syntax error. Adding anything makes it work, for example:
>>>>
>>>> class KUserOrGroupId
>>>> {
>>>> %TypeHeaderCode
>>>> #include <KCoreAddons/kuser.h>
>>>> %End
>>>> };
>>>>
>>>> is accepted. It would be nice to have support for this corner case.
>>>> Second, the syntax for template classes does not seem to work as I
>>>> expected. This example results in a syntax error, as does every
>>>> variation I could think of (including trying to match PyQt):
>>>>
>>>> template <typename T>
>>>> class KUserOrGroupId<T>
>>>> {
>>>> %TypeHeaderCode
>>>> #include <KCoreAddons/kuser.h>
>>>> %End
>>>> };
>>>>
>>>> Like the function case, I realise the implementation for this is not
>>>> trivial (templated methods and the like), but I cannot seem to make
>>>> the basic syntax work. It should, right?
>>>
>>> See...
>>>
>>> http://pyqt.sourceforge.net/Docs/sip4/specification_files.html#syntax-definition
>>>
>>> ...also look at the PyQt .sip files.
>>>
>>> In this case, omit 'typename'.
>>
>> I tried (having reviewed the syntax page and parser.y) several
>> variations such as this:
>>
>> ====
>> %Module test_template
>>
>> template <T>
>> class KUserOrGroupId<T>  <<< line 4
>> {
>> %TypeHeaderCode
>> #include <KCoreAddons/kuser.h>
>> %End
>> };
>> ====
>>
>> which does not work. However, it *does* work if I discard the "<T>"
>> from line 4, or use %MappedType. What is eluding me are the rules I
>> need to follow for references to T within the class. For example,
>> let's say the class contained a method with the signature:
>>
>>    void foo(T *bar);
>>
>> If I understand correctly, the semantics of passing T in are knowable,
>> but SIP does not like the "T", and I have not been able to work out
>> how the signature for foo should be written to get it past the syntax
>> errors. Is a template class able to support things like this (once I
>> implement the %MappedType)?
>
> I honestly can't remember if it's supposed to work or not. What's the error when SIP 'does not like the "T"'?
>
> I would actually approach it from the other end - first of all how do you want to represent KUserOrGroupId in Python?

The error from SIP is simply "syntax error" [1].

But you ask an apposite question and in truth, I don't yet know, yet.
The point is that SIP for KF5 (ad KDE generally) is a substantial
undertaking for which I am attempting to develop an automated approach
[2]. At this point, I'm trying to limit how deep I go in favour of
breadth and trying to get *some* bindings working.

Trying to get enough of the generated SIP to run through the syntax
phase at least seems important to me to ensure the overall automation
approach is sound (this is not something I consider proved yet). This
seems critical to me because the inability to sustain the maintenance
effort on PyKDE4 seems to me to be the root cause that KDE 5 has no
bindings.

It may be that this ends up being unrealistic, and I end up having to
go deep and perhaps generate manual code for some of the base classes
before anything useful can be made to work, but I'm not quite there
yet.

Thanks for all the help so far, it really is appreciated,

Shaheed

[1] This example is artificial and actually, AFICS, the real
KUserOrGroupId likely is not a very useful class...it just happens to
be one of the templated classes in the KF5 "sample" set.
=================
%Module test_template

template <T>
%MappedType KUserOrGroupId<T>
{
%TypeHeaderCode
#include <KCoreAddons/kuser.h>
%End
    void foo(T *bar);
};
%End
=================
$ sip test_template.sip
sip: test_template.sip:9: syntax error

[2] http://marc.info/?l=kde-bindings&m=145903148224117&w=2

>
> Phil