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Date: Mon, 3 Jun 2024 11:25:04 -0700
From: Boqun Feng <boqun.feng@gmail.com>
To: Alice Ryhl <aliceryhl@google.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>,
	=?iso-8859-1?Q?Bj=F6rn?= Roy Baron <bjorn3_gh@protonmail.com>,
	Benno Lossin <benno.lossin@proton.me>,
	Andreas Hindborg <a.hindborg@samsung.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Arve =?iso-8859-1?B?SGr4bm5lduVn?= <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
Subject: Re: [PATCH v4 4/6] rust: rbtree: add mutable iterator
Message-ID: <Zl4KgPuFn9HSmXen@boqun-archlinux>
References: <20240603-b4-rbtree-v4-0-308e43d6abfc@google.com>
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 <Zl4AVUqq8Hd-a230@boqun-archlinux>
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In-Reply-To: <CAH5fLggfMNcuu0KD13_K49NBXXWD133BB6uc5ph7xQi0WTxBZg@mail.gmail.com>

On Mon, Jun 03, 2024 at 07:52:36PM +0200, Alice Ryhl wrote:
> On Mon, Jun 3, 2024 at 7:42 PM Boqun Feng <boqun.feng@gmail.com> wrote:
> >
> > 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 and 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.
> 

You are probably right. But it's a bit pity that we miss the `Sync` +
`!Send` case :-/

Regards,
Boqun

> Alice