118 lines
3.5 KiB
Plaintext
118 lines
3.5 KiB
Plaintext
[section boost/python/wrapper.hpp]
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[section Introduction]
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To wrap a class T such that its virtual functions can be "overridden in Python"—so that the corresponding method of a Python derived class will be called when the virtual function is invoked from C++—you must create a C++ wrapper class derived from `T` that overrides those virtual functions so that they call into Python. This header contains classes that can be used to make that job easier.
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[endsect]
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[section Class `override`]
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Encapsulates a Python override of a C++ virtual function. An override object either holds a callable Python object or `None`.
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``
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namespace boost
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{
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class override : object
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{
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public:
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unspecified operator() const;
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template <class A0>
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unspecified operator(A0) const;
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template <class A0, class A1>
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unspecified operator(A0, A1) const;
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...
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template <class A0, class A1, ...class An>
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unspecified operator(A0, A1, ...An) const;
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};
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};
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``
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[endsect]
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[section Class `override` observer functions]
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``
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unspecified operator() const;
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template <class A0>
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unspecified operator(A0) const;
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template <class A0, class A1>
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unspecified operator(A0, A1) const;
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...
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template <class A0, class A1, ...class An>
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unspecified operator(A0, A1, ...An) const;
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``
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[variablelist
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[[Effects][If *this holds a callable Python object, it is invoked with the specified arguments in the manner specified here. Otherwise, throws [link high_level_components.boost_python_errors_hpp.class_error_already_set error_already_set].]]
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[[Returns][An object of unspecified type that holds the Python result of the invocation and, when converted to a C++ type R, attempts to convert that result object to R. If that conversion fails, throws [link high_level_components.boost_python_errors_hpp.class_error_already_set error_already_set].]]
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]
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[endsect]
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[section Class template `wrapper`]
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Deriving your wrapper class from both `T` and `wrapper<T>` makes writing that derived class easier.
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``
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namespace boost
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{
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class wrapper
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{
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protected:
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override get_override(char const* name) const;
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};
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};
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``
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[endsect]
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[section Class template `wrapper` observer functions]
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``override get_override(char const* name) const;``
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[variablelist
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[[Requires][name is a [link ntbs].]]
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[[Returns][If `*this` is the C++ base class subobject of a Python derived class instance that overrides the named function, returns an override object that delegates to the Python override. Otherwise, returns an override object that holds `None`.]]
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]
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[endsect]
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[section Example]
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``
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#include <boost/python/module.hpp>
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#include <boost/python/class.hpp>
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#include <boost/python/wrapper.hpp>
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#include <boost/python/call.hpp>
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using namespace boost::python;
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// Class with one pure virtual function
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struct P
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{
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virtual ~P(){}
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virtual char const* f() = 0;
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char const* g() { return "P::g()"; }
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};
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struct PCallback : P, wrapper<P>
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{
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char const* f()
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{
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return this->get_override("f")();
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}
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};
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// Class with one non-pure virtual function
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struct A
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{
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virtual ~A(){}
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virtual char const* f() { return "A::f()"; }
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};
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struct ACallback : A, wrapper<A>
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{
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char const* f()
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{
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if (override f = this->get_override("f"))
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return f();
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return A::f();
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}
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char const* default_f() { return this->A::f(); }
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};
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BOOST_PYTHON_MODULE_INIT(polymorphism)
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{
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class_<PCallback,boost::noncopyable>("P")
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.def("f", pure_virtual(&P::f))
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;
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class_<ACallback,boost::noncopyable>("A")
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.def("f", &A::f, &ACallback::default_f)
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;
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}
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``
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[endsect]
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[endsect]
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