Re: [PATCH v3 08/13] rust: init: add `stack_pin_init!` macro

[Alice Ryhl]

On 3/30/23 17:19, Benno Lossin wrote:
> On 30.03.23 17:00, Alice Ryhl wrote:
> > On 3/30/23 00:33, y86-dev@xxxxxxxxxxxxxx wrote:
> > > From: Benno Lossin <y86-dev@xxxxxxxxxxxxxx>
> > >
> > > The `stack_pin_init!` macro allows pin-initializing a value on the
> > > stack. It accepts a `impl PinInit<T, E>` to initialize a `T`. It allows
> > > propagating any errors via `?` or handling it normally via `match`.
> > >
> > > Signed-off-by: Benno Lossin <y86-dev@xxxxxxxxxxxxxx>
> >
> > Reviewed-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>
> >
> > > ---
> > > +#[macro_export]
> > > +macro_rules! stack_pin_init {
> > > +    (let $var:ident $(: $t:ty)? = $val:expr) => {
> > > +        let mut $var = $crate::init::__internal::StackInit$(::<$t>)?::uninit();
> > > +        let mut $var = {
> > > +            let val = $val;
> > > +            unsafe { $crate::init::__internal::StackInit::init(&mut $var, val) }
> > > +        };
> > > +    };
> > > +    (let $var:ident $(: $t:ty)? =? $val:expr) => {
> > > +        let mut $var = $crate::init::__internal::StackInit$(::<$t>)?::uninit();
> > > +        let mut $var = {
> > > +            let val = $val;
> > > +            unsafe { $crate::init::__internal::StackInit::init(&mut $var, val)? }
> > > +        };
> > > +    };
> > > +}
> >
> > This will be inconvenient to use if the initializer is infallible and is
> > used inside an infallible function. However, I'm not sure what a better
> > alternative would be. Perhaps we should have three variants?
>
> That could be an option, any ideas for the syntax though? Or should it
> be a different macro like `stack_pin_init!` and `try_stack_pin_init!`?

You've also split up the other macros into a fallible and infallible 
version, so I think the same would be fine here. Perhaps use 
`stack_pin_try_init!` as the name?

> > Also, maybe a `<-` rather than `=` would be more consistent?
>
> That is sadly not possible, since `<-` is not allowed after `ty` fragments.
>
> > Anyway, I don't think this should block the PR. We can revisit it later
> > if it becomes a problem.
>
> Sure.
>
> --
> Cheers,
> Benno