# __nocast vs __bitwise `__nocast` warns about explicit or implicit casting to different types. HOWEVER, it doesn't consider two 32-bit integers to be different types, so a `__nocast int` type may be returned as a regular `int` type and then the `__nocast` is lost. So `__nocast` on integer types is usually not that powerful. It just gets lost too easily. It's more useful for things like pointers. It also doesn't warn about the mixing: you can add integers to `__nocast` integer types, and it's not really considered anything wrong. `__bitwise` ends up being a *stronger integer separation*. That one doesn't allow you to mix with non-bitwise integers, so now it's much harder to lose the type by mistake. So the basic rule is: - `__nocast` on its own tends to be more useful for *big* integers that still need to act like integers, but you want to make it much less likely that they get truncated by mistake. So a 64-bit integer that you don't want to mistakenly/silently be returned as `int`, for example. But they mix well with random integer types, so you can add to them etc without using anything special. However, that mixing also means that the `__nocast` really gets lost fairly easily. - `__bitwise` is for *unique types* that cannot be mixed with other types, and that you'd never want to just use as a random integer (the integer `0` is special, though, and gets silently accepted - it's kind of like `NULL` for pointers). So `gfp_t` or the `safe endianness` types would be `__bitwise`: you can only operate on them by doing specific operations that know about *that* particular type. Generally, you want `__bitwise` if you are looking for type safety. `__nocast` really is pretty weak. ## Reference: * Linus' e-mail about `__nocast` vs `__bitwise`: