Still many C++ codes are so difficult for me to understand..
Below is a code snippet from dlib (http://dlib.net file : dlib/external/pybind11/include/pybind11/pybind11.h)
It's a member function definition of class cpp_function
and I didn't try to understand the code(no time to do that..that's sad..). I can't understand the syntax in the line I put *** this line!
comment at below. I understand the lambda function(unnamed function), so is it assigning a function pointer to rec->impl
, the function taking function_call &call
as argument and returning handle
? So, it looks like defining a function and at the same time assigning the function pointer to a variable. Having asked it, it looks so now.. Please someone confirm this.
void initialize(Func &&f, Return (*)(Args...), const Extra&... extra) {
using namespace detail;
struct capture { remove_reference_t<Func> f; };
...
rec->impl = [](function_call &call) -> handle { // <=== *** this line!
cast_in args_converter;
/* Try to cast the function arguments into the C++ domain */
if (!args_converter.load_args(call))
return PYBIND11_TRY_NEXT_OVERLOAD;
/* Invoke call policy pre-call hook */
process_attributes<Extra...>::precall(call);
/* Get a pointer to the capture object */
auto data = (sizeof(capture) <= sizeof(call.func.data)
? &call.func.data : call.func.data[0]);
capture *cap = const_cast<capture *>(reinterpret_cast<const capture *>(data));
/* Override policy for rvalues -- usually to enforce rvp::move on an rvalue */
const auto policy = return_value_policy_override<Return>::policy(call.func.policy);
/* Function scope guard -- defaults to the compile-to-nothing `void_type` */
using Guard = extract_guard_t<Extra...>;
/* Perform the function call */
handle result = cast_out::cast(
std::move(args_converter).template call<Return, Guard>(cap->f), policy, call.parent);
/* Invoke call policy post-call hook */
process_attributes<Extra...>::postcall(call, result);
return result;
};
...
using FunctionType = Return (*)(Args...);
constexpr bool is_function_ptr =
std::is_convertible<Func, FunctionType>::value &&
sizeof(capture) == sizeof(void *);
if (is_function_ptr) {
rec->is_stateless = true;
rec->data[1] = const_cast<void *>(reinterpret_cast<const void *>(&typeid(FunctionType)));
}
}
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