as_tuple

Definition

Class as_tuple is a model of ResultConverterGenerator which can be used to wrap C++ functions returning a pointer to arrays with fixed size. The policy will construct a Python tuple from the array and handle the array memory.

Example

 struct vector3{
     ...

     float* clone_raw_data() const{
         float* values = new float[3];
         //copy values
         return values;
     }

     const flow* get_raw_data() const{
         return m_values;
     }

 private:
     float m_values[3];
 };

namespace bpl = boost::python;
namespace pypp_cp = pyplusplus::call_policies;
BOOST_PYTHON_MODULE(my_module){
  bpl::class_< vector3 >( "vector3" )
      .def( "clone_raw_data"
            , &::vector3::clone_raw_data
            , bpl::return_value_policy< pypp_cp::arrays::as_tuple< 3, pypp_cp::memory_managers::delete_ > >() )
      .def( "get_raw_data"
            , &::vector3::get_raw_data
            , bpl::return_value_policy< pypp_cp::arrays::as_tuple< 3, pypp_cp::memory_managers::none > >() ) );
}

as_tuple class

as_tuple is a template class that takes few arguments:

1. the array size - compile time constant
2. memory management policy - a class, which will manage the return value. There are two built-in memory managers:
   • delete_ - the array will be deleted after it was copied to tuple, using operator delete[]
   • none - do nothing

The Py++ code is slightly different from the C++ one, but it is definitely shorter:

from pyplusplus import module_builder
from pyplusplus.module_builder import call_policies

mb = module_builder.module_builder_t( ... )
mb.member_function( 'clone_raw_data' ).call_policies \
    = call_policies.convert_array_to_tuple( 3, call_policies.memory_managers.delete_ )
mb.member_function( 'get_raw_data' ).call_policies \
    = call_policies.convert_array_to_tuple( 3, call_policies.memory_managers.none )