[C++-sig] Exporting an abstract class with virtual bool operator()(int)=0

[pedro]

Achim H. a écrit :
> Hi!
>   

Hi!
First of all, thanks for you answer, Achim.

> IMHO, boost::python doesn't know that condition_Wrap is derived from 
> condition, you'd have to mention that in the class_<>() statement.
>
>   
Could you be more precise about this, please? How would you mention this ...
I just followed the boost.python tutorial section about "Exposing 
Classes > Class Virtual Functions" and
they proceed with class_<> in the way I do.

Thanks again.
Pedro.
> Achim.
>
> Pedro Crespo Valero wrote:
>
>   
>> Hello everybody,
>>
>> I would like to export to python a function object that acts as a
>> predicate to specify "what
>> to filter" in my member function A::filter(pred). The point is that I
>> would like to define the predicates
>> in python so I decided to use an abstact class that I call "condition".
>> I include a little example below to clarify my problem.
>> Everything goes well and compiles but as you will see below I have
>> problems when I use it in python.
>> I would really appreciate if you could clarify me why is this happening
>> and some clue to solve it,
>> Thank you very much in advance for you help.
>> Pedro.
>>
>>
>> ////////////////////////////////////////////
>>
>> #include <boost/python.hpp>
>> #include <vector>
>>
>> // An abstract class
>> struct condition{
>>     virtual bool operator()(const int ii)=0;
>>     virtual ~condition(){}
>> };
>>
>> const int vals[]={1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
>>
>> class A{
>> private:
>>     std::vector<int> values_;
>>     std::vector<int> fvalues_;
>> public:
>>     A():values_(vals[0],vals[9]+1), fvalues_(0){}
>>
>>     void filter(condition& pred)
>>     {
>>         fvalues_.resize(0);
>>         for (std::size_t i=0; i<values_.size(); i++){
>>             if (pred(values_[i]))
>>                 fvalues_.push_back(values_[i]);
>>         }
>>     }
>>
>> };
>>
>> //::::::::::::::::::::BOOST::PYTHON in action:::::::::::::::::::::::::
>> using namespace boost::python;
>>
>> struct condition_Wrap: condition, wrapper<condition>{
>>     bool operator()(const int ii){ return
>> call<bool>(this->get_override("operator()").ptr(),ii);}
>> };
>>
>> BOOST_PYTHON_MODULE(test2py)
>> {
>>     class_<condition_Wrap, boost::noncopyable>("condition")
>>         .def("__call__", pure_virtual(&condition::operator()))
>>         ;
>>
>>     class_<A>("A")
>>         .def("filter",&A::filter)
>>         ;
>> }
>>
>>
>> In python::::::::::::::::::::::::::::::::::::::::::::::
>>
>> from test2py import *
>>
>> # inherit condition and override __call__
>> class less_than(condition):
>>     def __init__(self,NoMx):
>>         self.max=NoMx
>>
>>     def __call__(self,n):
>>         return (n<self.max)
>>
>>
>> x=A()
>> x.filter(less_than(5))
>>
>>
>> And then BOOM!!!!  the output is the following....
>>
>> Traceback (most recent call last):
>>   File "d:\My_Documents\pysource\test.py", line 19, in ?
>>     x.filter(less_than(5))
>> ArgumentError: Python argument types in
>>     A.filter(A, less_than)
>> did not match C++ signature:
>>     filter(class A {lvalue}, struct condition {lvalue})
>>
>>
>> Thanks again!!
>> Long life to Boost.python !!!  :-D
>>
>>     
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