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Message-ID: <CAH5fLghO8v0wn-uCx1u_zojPLdDH_RMn4BXxLB1ZMJjfpTkbAw@mail.gmail.com>
Date: Thu, 1 Aug 2024 17:10:22 +0200
From: Alice Ryhl <aliceryhl@...gle.com>
To: Danilo Krummrich <dakr@...nel.org>
Cc: ojeda@...nel.org, alex.gaynor@...il.com, wedsonaf@...il.com,
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Subject: Re: [PATCH v3 17/25] rust: alloc: implement `collect` for `IntoIter`
On Thu, Aug 1, 2024 at 2:08 AM Danilo Krummrich <dakr@...nel.org> wrote:
>
> Currently, we can't implement `FromIterator`. There are a couple of
> issues with this trait in the kernel, namely:
>
> - Rust's specialization feature is unstable. This prevents us to
> optimze for the special case where `I::IntoIter` equals `Vec`'s
> `IntoIter` type.
> - We also can't use `I::IntoIter`'s type ID either to work around this,
> since `FromIterator` doesn't require this type to be `'static`.
> - `FromIterator::from_iter` does return `Self` instead of
> `Result<Self, AllocError>`, hence we can't properly handle allocation
> failures.
> - Neither `Iterator::collect` nor `FromIterator::from_iter` can handle
> additional allocation flags.
>
> Instead, provide `IntoIter::collect`, such that we can at least convert
> `IntoIter` into a `Vec` again.
>
> Signed-off-by: Danilo Krummrich <dakr@...nel.org>
I'm not convinced a collect implementation specific to IntoIter is necessary?
> +
> + // SAFETY: `buf` points to the start of the backing buffer and `len` is guaranteed to be
> + // smaller than `cap`. Depending on `alloc` this operation may shrink the buffer or leaves
> + // it as it is.
> + ptr = match unsafe { A::realloc(Some(buf.cast()), layout, flags) } {
Why would you shrink it? You can just keep the capacity.
Alice
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