[PyQt] downcast a base class to its template subclass

[Phil Thompson]

On Tue, 2 Nov 2010 10:55:51 -0700, Qin Shen <jeanshen at tippett.com> wrote:
> Hi Phil,
> 
> Phil Thompson wrote:
>> On Mon, 1 Nov 2010 17:26:41 -0700, Qin Shen <jeanshen at tippett.com>
wrote:
>>   
>>> Hi,
>>>
>>> In my non-template base class' .sip file, I used
%ConvertToSubClassCode 
>>> directive
>>> to downcast the base class type to its sub-class. If the sub-class is 
>>> not a template,
>>> it all works fine. Now I need to derive a template sub-class from the 
>>> base class,
>>> the sipFindType() won't work because there isn't any Python class 
>>> implemented
>>> for the templated sub-class. What should I do in this case?
>>>     
>>
>> So how is the template sub-class implemented in Python? Your
>> %ConvertToSubClassCode will need to explicitly check for the template
>> sub-class and return the appropriate Python type.
>>   
> The .sip file of the template sub-class is based on its C++ .h header
file.
> Its implementation in the .sip file has been omitted since I thought I 
> don't
> need to put any implementation in the .sip file as its C++ header file
has
> been properly included.
> 
> When you asked how is the template sub-class implemented in Python, did
you
> mean that I need to put the C++ style implementation in .sip as well?
> 
> Do I need to use %MappedType to convert the template sub-class to/from a

> Python
> type. For a non-template class, sip usually generates a .cpp file for it

> as well
> as a corresponding sipType_BLAH. In the case of a template class,
neither
> was generated. I don't see a direct type match between a Python type and
> any
> specialization of the template sub-class, and no sipType_ is generated
for
> the template class, how am I supposed to convert the type?

Any C++ template must eventually be implemented using a %MappedType -
that's where you decide what Python type will be used to represent the C++
type.

> Do you have any example on this?

There are lots of examples in PyQt - qlist.sip is probably the most
comprehensive.

Phil