linux-kernel - Re: [PATCH v1 1/2] rust: time: Rename Delta's methods as_micros_ceil and as

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Message-ID: <aFKMXqak-mHraxU_@google.com>
Date: Wed, 18 Jun 2025 09:52:30 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
Cc: FUJITA Tomonori <fujita.tomonori@...il.com>, a.hindborg@...nel.org, alex.gaynor@...il.com, 
	ojeda@...nel.org, anna-maria@...utronix.de, bjorn3_gh@...tonmail.com, 
	boqun.feng@...il.com, dakr@...nel.org, frederic@...nel.org, gary@...yguo.net, 
	jstultz@...gle.com, linux-kernel@...r.kernel.org, lossin@...nel.org, 
	lyude@...hat.com, rust-for-linux@...r.kernel.org, sboyd@...nel.org, 
	tglx@...utronix.de, tmgross@...ch.edu
Subject: Re: [PATCH v1 1/2] rust: time: Rename Delta's methods as_micros_ceil
 and as_millis

On Wed, Jun 18, 2025 at 11:29:26AM +0200, Miguel Ojeda wrote:
> On Wed, Jun 18, 2025 at 10:05 AM Alice Ryhl <aliceryhl@...gle.com> wrote:
> >
> > Why are we renaming them? The stdlib always uses as_* or to_* for copy
> > types. In my mind, into_* means that you want to emphasize that you are
> > performing a transformation that consumes self and transfers ownership
> > of some resource in the process.
> >
> > See the api guidelines:
> > https://rust-lang.github.io/api-guidelines/naming.html#ad-hoc-conversions-follow-as_-to_-into_-conventions-c-conv
> 
> We may be going in circles here... I think the confusion is all on
> what to do for "owned -> owned" `Copy` non-expensive conversions.
> 
> I think Tomo sent a patch to change the `as_` and `is_` methods to
> take `&self` to be consistent with the guidelines, since they say
> there is no "owned -> owned" case for `as_`. Then you mentioned that
> `self` is OK and Andreas agreed, and I guess Tomo ended up with
> `into_` since `to_` is only for the expensive case, even though it is
> not meant for `Copy` types.
> 
> In other words, either we say in the kernel we are OK with `as_` for
> "owned -> owned" too, or we take `&self`.
> 
> Did I get that right, everyone?

Yeah I think using as_* naming for cases other than borrowed->borrowed
is relatively common for Copy types. Looking at the stdlib, the rules
I'm seeing are more or less these:

First, if the method is expensive the naming is to_* or a verb without a
prefix. We only use into_* for expensive operations if the call also
transfers ownership of some resource. Example: CStr::to_bytes()

Otherwise, if the method is something that looks inside the type (i.e.
it peels away a layer of abstraction), then we using as_* naming. Or we
might use a noun with no prefix if we want it to feel like a field
access. Example: Duration::as_millis()

On the other hand, if the method transforms the value while staying at
the same layer of abstraction, then we may call the method to_* (or just
use a verb without a prefix). Example: f64::to_radians()

Alice