Function lua_touserdatatagged 

pub unsafe extern "C-unwind" fn lua_touserdatatagged(
    L: *mut lua_State,
    idx: c_int,
    tag: c_int,
) -> *mut c_void

Returns the pointer to the userdata at the given index if it has the given tag.

If the value at the given index is not a userdata, or if it does not have the given tag, this function will return null. Otherwise, it will return a pointer to the userdata.