diff options
| -rw-r--r-- | src/libcore/ffi.rs | 17 |
1 files changed, 10 insertions, 7 deletions
diff --git a/src/libcore/ffi.rs b/src/libcore/ffi.rs index 0717a88b6b8..b50e4f3c289 100644 --- a/src/libcore/ffi.rs +++ b/src/libcore/ffi.rs @@ -12,24 +12,27 @@ use ::fmt; /// and `*mut c_void` is equivalent to C's `void*`. That said, this is /// *not* the same as C's `void` return type, which is Rust's `()` type. /// -/// Ideally, this type would be equivalent to [`!`], but currently it may -/// be more ideal to use `c_void` for FFI purposes. +/// To model pointers to opaque types in FFI, until `extern type` is +/// stabilized, it is recommended to use a newtype wrapper around an empty +/// byte array. See the [Nomicon] for details. /// -/// [`!`]: ../../std/primitive.never.html /// [pointer]: ../../std/primitive.pointer.html +/// [Nomicon]: https://doc.rust-lang.org/nomicon/ffi.html#representing-opaque-structs // N.B., for LLVM to recognize the void pointer type and by extension // functions like malloc(), we need to have it represented as i8* in // LLVM bitcode. The enum used here ensures this and prevents misuse -// of the "raw" type by only having private variants.. We need two +// of the "raw" type by only having private variants. We need two // variants, because the compiler complains about the repr attribute -// otherwise. +// otherwise and we need at least one variant as otherwise the enum +// would be uninhabited and at least dereferencing such pointers would +// be UB. #[repr(u8)] #[stable(feature = "raw_os", since = "1.1.0")] pub enum c_void { - #[unstable(feature = "c_void_variant", reason = "should not have to exist", + #[unstable(feature = "c_void_variant", reason = "temporary implementation detail", issue = "0")] #[doc(hidden)] __variant1, - #[unstable(feature = "c_void_variant", reason = "should not have to exist", + #[unstable(feature = "c_void_variant", reason = "temporary implementation detail", issue = "0")] #[doc(hidden)] __variant2, } |