Answer by HolyBlackCat for How to wrap class method to C function if it exists and to `nullptr` if it do not exist?

There are several ways of doing this using requires, depending on how strictly you want to check the method.

E.g.:

device_module_info cls{};if constexpr (requires(DeviceHandleImpl h, off_t pos, void *buffer, size_t *_length){    h.Read(pos, buffer, _length);})    cls.read = /*some lambda*/;

This only checks that the method exists and that the argument types are correct. If the return type is wrong, you get a compilation error.

You could check the return type too. This checks for exact match:

if constexpr (requires(DeviceHandleImpl h, off_t pos, void *buffer, size_t *_length) {    requires std::same_as<status_t, decltype(h.Read(pos, buffer, _length))>;})    cls.read = /*some lambda*/;

Or this checks for convertibility:

if constexpr (requires(DeviceHandleImpl h, off_t pos, void *buffer, size_t *_length) {    { h.Read(pos, buffer, _length) } -> std::convertible_to<status_t>;})    cls.read = /*some lambda*/;

All of the approaches above allow implicit conversions in arguments. I don't think there's an easy way to prevent that.