使用shared_ptr通过boost.python将base抽象为holder

Question

我们小组正在使用C++开发一个数字框架.我们现在想要将我们框架的基本部分包装在Python中.我们选择的武器是Boost.Python,因为我们已经将Boost用于其他目的.我们只使用smart_ptrs来支持多态性.以下代码段是我们如何应用策略模式的简单示例:

#include <boost/shared_ptr.hpp>
struct AbsStrategy
{
  virtual std::string talk( ) = 0;
};

typedef boost::shared_ptr<AbsStrategy> StrategyPtr;

struct Foo : AbsStrategy
{
  std::string talk( )
  {
    return "I am a Foo!";
  }
};

struct Bar : AbsStrategy
{
  std::string talk( )
  {
    return "I am a Bar!";
  }
};

struct Client
{
  Client( StrategyPtr strategy ) :
          myStrategy( strategy )
  {
  }

  bool checkStrategy( StrategyPtr strategy )
  {
    return ( strategy == myStrategy );
  }

  StrategyPtr myStrategy;
};

如果我像这样用Boost.Python包装整个东西

#include <boost/python.hpp>
using namespace boost::python;

BOOST_PYTHON_MODULE( BoostPython )
{
  class_<Foo>( "Foo" )
      .def( "talk", &Foo::talk );

  class_<Bar>( "Bar" )
      .def( "talk", &Bar::talk );

  class_<Client>( "Client", init<StrategyPtr>( ) )
      .def( "checkStrategy", &Client::checkStrategy );
}

编译期间会弹出以下警告

C:/boost/include/boost-1_51/boost/python/object/instance.hpp:14:36: warning: type attributes ignored after type is already defined [-Wattributes]

当我尝试在python中使用包装器时,我收到以下错误

>>> from BoostPython import *
>>> foo = Foo()
>>> bar = Bar()
>>> client = Client(foo)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
Boost.Python.ArgumentError: Python argument types in
    Tree.__init__(Tree, Foo)
did not match C++ signature:
    __init__(_object*, boost::shared_ptr<AbsStrategy>)
>>> client = Client(bar)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
Boost.Python.ArgumentError: Python argument types in
    Tree.__init__(Tree, Bar)
did not match C++ signature:
    __init__(_object*, boost::shared_ptr<AbsStrategy>)

在不改变我们的框架的情况下,让整个事情发挥作用缺少什么？包装纸当然可以自由调整.

Answer 1

好吧，我找到了解决方案。必须implicitly_convertible在模块声明中使用，如下所示。

#include <boost/python.hpp>
using namespace boost::python;

BOOST_PYTHON_MODULE( BoostPython )
{
  class_<Foo>( "Foo" )
      .def( "talk", &Foo::talk );

  class_<Bar>( "Bar" )
      .def( "talk", &Bar::talk );

  class_<Client>( "Client", init<StrategyPtr>( ) )
      .def( "checkStrategy", &Client::checkStrategy );

  implicitly_convertible<boost::shared_ptr<Foo> , StrategyPtr>();
  implicitly_convertible<boost::shared_ptr<Bar> , StrategyPtr>();
}