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;
};

如果我像这样使用Boost.Python包装整个事物

#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的缺失是什么？包装纸当然可以自由调整。

Answer 1

好的，我找到了解决方案。必须在模块声明中使用implicitly_convertible，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>();
}

使用shared_ptr通过boost.python将base抽象为holder

1 个答案: