[PyQt] Empty and template classes

[Shaheed Haque]

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)?

Thanks, Shaheed