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perf: add reference_internal policy for const-ref returns #182

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perf: add reference_internal policy for const-ref returns #182

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17 changes: 15 additions & 2 deletions gtwrap/pybind_wrapper.py
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Original file line number Diff line number Diff line change
Expand Up @@ -251,6 +251,17 @@ def _wrap_method(self,
method,
(parser.StaticMethod, instantiator.InstantiatedStaticMethod))
return_void = method.return_type.is_void()
return_ref = getattr(
getattr(method.return_type, 'type1', None), 'is_ref', False)

# For methods returning const T&, use reference_internal policy
# to avoid unnecessary copies and keep the returned reference alive.
if return_ref and is_method:
lambda_ret = ' -> const auto&'
ref_policy = ', py::return_value_policy::reference_internal'
else:
lambda_ret = ''
ref_policy = ''

caller = cpp_class + "::" if not is_method else "self->"
function_call = ('{opt_return} {caller}{method_name}'
Expand All @@ -263,10 +274,10 @@ def _wrap_method(self,

result = (
'{prefix}.{cdef}("{py_method}",'
'[]({opt_self}{opt_comma}{args_signature_with_names}){{'
'[]({opt_self}{opt_comma}{args_signature_with_names}){lambda_ret}{{'
'{function_call}'
'}}'
'{py_args_names}{docstring}){suffix}'.format(
'{ref_policy}{py_args_names}{docstring}){suffix}'.format(
prefix=prefix,
cdef="def_static" if is_static else "def",
py_method=py_method,
Expand All @@ -275,7 +286,9 @@ def _wrap_method(self,
opt_comma=', '
if is_method and args_signature_with_names else '',
args_signature_with_names=args_signature_with_names,
lambda_ret=lambda_ret,
function_call=function_call,
ref_policy=ref_policy,
py_args_names=py_args_names,
suffix=suffix,
# Try to get the function's docstring from the Doxygen XML.
Expand Down
4 changes: 2 additions & 2 deletions tests/expected/python/class_pybind.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -43,8 +43,8 @@ PYBIND11_MODULE(class_py, m_) {
.def("return_matrix1",[](Test* self, const gtsam::Matrix& value){return self->return_matrix1(value);}, py::arg("value"))
.def("return_vector2",[](Test* self, const gtsam::Vector& value){return self->return_vector2(value);}, py::arg("value"))
.def("return_matrix2",[](Test* self, const gtsam::Matrix& value){return self->return_matrix2(value);}, py::arg("value"))
.def("return_vector2",[](Test* self, const gtsam::Vector& value){return self->return_vector2(value);}, py::arg("value"))
.def("return_matrix2",[](Test* self, const gtsam::Matrix& value){return self->return_matrix2(value);}, py::arg("value"))
.def("return_vector2",[](Test* self, const gtsam::Vector& value) -> const auto&{return self->return_vector2(value);}, py::return_value_policy::reference_internal, py::arg("value"))
.def("return_matrix2",[](Test* self, const gtsam::Matrix& value) -> const auto&{return self->return_matrix2(value);}, py::return_value_policy::reference_internal, py::arg("value"))
.def("arg_EigenConstRef",[](Test* self, const gtsam::Matrix& value){ self->arg_EigenConstRef(value);}, py::arg("value"))
.def("push_back",[](Test* self, gtsam::Key key){ self->push_back(key);}, py::arg("key"))
.def("return_field",[](Test* self, const Test& t){return self->return_field(t);}, py::arg("t"))
Expand Down