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From: Alice Ryhl <aliceryhl@google.com>
Date: Mon, 3 Jun 2024 19:52:36 +0200
Message-ID: <CAH5fLggfMNcuu0KD13_K49NBXXWD133BB6uc5ph7xQi0WTxBZg@mail.gmail.com>
Subject: Re: [PATCH v4 4/6] rust: rbtree: add mutable iterator
To: Boqun Feng <boqun.feng@gmail.com>
Cc: Matt Gilbride <mattgilbride@google.com>, Miguel Ojeda <ojeda@kernel.org>, 
	Alex Gaynor <alex.gaynor@gmail.com>, Wedson Almeida Filho <wedsonaf@gmail.com>, Gary Guo <gary@garyguo.net>, 
	=?UTF-8?Q?Bj=C3=B6rn_Roy_Baron?= <bjorn3_gh@protonmail.com>, 
	Benno Lossin <benno.lossin@proton.me>, Andreas Hindborg <a.hindborg@samsung.com>, 
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>, =?UTF-8?B?QXJ2ZSBIasO4bm5ldsOlZw==?= <arve@android.com>, 
	Todd Kjos <tkjos@android.com>, Martijn Coenen <maco@android.com>, 
	Joel Fernandes <joel@joelfernandes.org>, Carlos Llamas <cmllamas@google.com>, 
	Suren Baghdasaryan <surenb@google.com>, Christian Brauner <brauner@kernel.org>, Rob Landley <rob@landley.net>, 
	Davidlohr Bueso <dave@stgolabs.net>, Michel Lespinasse <michel@lespinasse.org>, 
	rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org
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On Mon, Jun 3, 2024 at 7:42=E2=80=AFPM Boqun Feng <boqun.feng@gmail.com> wr=
ote:
>
> On Mon, Jun 03, 2024 at 04:05:19PM +0000, Matt Gilbride wrote:
> [...]
> > +/// A mutable iterator over the nodes of a [`RBTree`].
> > +///
> > +/// Instances are created by calling [`RBTree::iter_mut`].
> > +pub struct IterMut<'a, K, V> {
> > +    _tree: PhantomData<&'a mut RBTree<K, V>>,
> > +    iter_raw: IterRaw<K, V>,
> > +}
> > +
> > +// SAFETY: The [`RBTreeIterator`] gives out mutable references to K an=
d V, so it has the same
>
> s/RBTreeIterator/IterMut ?
>
> Also `IterMut` doesn't give out mutable references to K, which makes
> me think...
>
> > +// thread safety requirements as mutable references.
> > +unsafe impl<'a, K: Send, V: Send> Send for IterMut<'a, K, V> {}
> > +
>
> we can lose the constrains to `K: Sync`, right?

Either Send or Sync would be valid here, but almost all types that are
Sync are also Send, but the opposite is not the case. So I wouldn't
consider that to be loosening the constrain.

Alice