PyBindConverter : Add new class for PyBind/Boost interoperability

This is essentially the same as the one we've used in Gaffer for interfacing with OpenColorIO bindings for a little while now.

Author: johnhaddon

Changes

@@ -1,6 +1,11 @@
 10.5.x.x (relative to 10.5.4.2)
 ========
 
+Features
+--------
+
+- PyBindConverter : Added new class providing interoperability between Boost Python bindings and PyBind11 bindings.
+
 Improvements
 ------------
 

include/IECorePython/PyBindConverter.h

@@ -0,0 +1,102 @@
+
+//////////////////////////////////////////////////////////////////////////
+//
+//  Copyright (c) 2024, Cinesite VFX Ltd. All rights reserved.
+//
+//  Redistribution and use in source and binary forms, with or without
+//  modification, are permitted provided that the following conditions are
+//  met:
+//
+//      * Redistributions of source code must retain the above
+//        copyright notice, this list of conditions and the following
+//        disclaimer.
+//
+//      * Redistributions in binary form must reproduce the above
+//        copyright notice, this list of conditions and the following
+//        disclaimer in the documentation and/or other materials provided with
+//        the distribution.
+//
+//      * Neither the name of John Haddon nor the names of
+//        any other contributors to this software may be used to endorse or
+//        promote products derived from this software without specific prior
+//        written permission.
+//
+//  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
+//  IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
+//  THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+//  PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+//  CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+//  EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+//  PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+//  PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+//  LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+//  NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+//  SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+//
+//////////////////////////////////////////////////////////////////////////
+
+#ifndef IECOREPYTHON_PYBINDCONVERTER_H
+#define IECOREPYTHON_PYBINDCONVERTER_H
+
+#include "boost/python.hpp"
+
+#include "pybind11/pybind11.h"
+
+namespace IECorePython
+{
+
+// Registers `boost::python` converters for types
+// wrapped using PyBind11.
+template<typename T>
+struct PyBindConverter
+{
+
+	static void registerConverters()
+	{
+		boost::python::to_python_converter<T, ToPyBind>();
+		boost::python::converter::registry::push_back(
+			&FromPyBind::convertible,
+			&FromPyBind::construct,
+			boost::python::type_id<T>()
+		);
+	}
+
+	private :
+
+		struct ToPyBind
+		{
+			static PyObject *convert( const T &t )
+			{
+				pybind11::object o = pybind11::cast( t );
+				Py_INCREF( o.ptr() );
+				return o.ptr();
+			}
+		};
+
+		struct FromPyBind
+		{
+
+			static void *convertible( PyObject *object )
+			{
+				pybind11::handle handle( object );
+				return handle.cast<T>() ? object : nullptr;
+			}
+
+			static void construct( PyObject *object, boost::python::converter::rvalue_from_python_stage1_data *data )
+			{
+				void *storage = ( ( boost::python::converter::rvalue_from_python_storage<T> * ) data )->storage.bytes;
+				T *t = new( storage ) T;
+				data->convertible = storage;
+
+				pybind11::handle handle( object );
+				*t = handle.cast<T>();
+			}
+
+		};
+
+};
+
+} // namespace IECorePython
+
+#endif // IECOREPYTHON_PYBINDCONVERTER_H
+