pub type lua_Alloc = Option<extern "C" fn(ud: *mut c_void, ptr: *mut c_void, osize: size_t, nsize: size_t) -> *mut c_void>;
enum lua_Alloc { None, Some(extern "C" fn(*mut c_void, *mut c_void, usize, usize) -> *mut c_void), }
No value.
Some value of type T.
T