From 5eafae22ceb0e4fae835a5eb7518a55e75061e20 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Sebastian=20Dr=C3=B6ge?= Date: Fri, 7 Dec 2018 16:18:38 +0200 Subject: [PATCH] Remove confusing comment about ideally using `!` for `c_void` Using `!` for `c_void` would have the problem that pointers and potentially references to an uninhabited type would be created, and at least for references this is UB. Also document in addition that newtype wrappers around `c_void` are not recommended for representing opaque types (as a workaround for `extern type` not being stable) but instead refer to the Nomicon. --- src/libcore/ffi.rs | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/src/libcore/ffi.rs b/src/libcore/ffi.rs index d7a112eb90df..02e92af85345 100644 --- a/src/libcore/ffi.rs +++ b/src/libcore/ffi.rs @@ -13,11 +13,12 @@ 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