From 2dde1c8b04a5c415912bc3ffa8b677eb364dbcb7 Mon Sep 17 00:00:00 2001 From: Tamir Duberstein Date: Thu, 7 Nov 2024 05:36:46 -0500 Subject: [PATCH] rust: sync: document `PhantomData` in `Arc` Add a comment explaining the relevant semantics of `PhantomData`. This should help future readers who may, as I did, assume that this field is redundant at first glance. Signed-off-by: Tamir Duberstein Reviewed-by: Alice Ryhl Link: https://lore.kernel.org/r/20241107-simplify-arc-v2-1-7256e638aac1@gmail.com Signed-off-by: Miguel Ojeda --- rust/kernel/sync/arc.rs | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs index fa4509406ee90..9f0b04400e8e5 100644 --- a/rust/kernel/sync/arc.rs +++ b/rust/kernel/sync/arc.rs @@ -127,6 +127,14 @@ mod std_vendor; /// ``` pub struct Arc { ptr: NonNull>, + // NB: this informs dropck that objects of type `ArcInner` may be used in ` as + // Drop>::drop`. Note that dropck already assumes that objects of type `T` may be used in + // ` as Drop>::drop` and the distinction between `T` and `ArcInner` is not presently + // meaningful with respect to dropck - but this may change in the future so this is left here + // out of an abundance of caution. + // + // See https://doc.rust-lang.org/nomicon/phantom-data.html#generic-parameters-and-drop-checking + // for more detail on the semantics of dropck in the presence of `PhantomData`. _p: PhantomData>, } -- 2.47.2