Re: [PATCH 1/6] rust: alloc: add Vec::push_init

[Danilo Krummrich]

On Mon Aug 17, 2026 at 2:56 PM CEST, Eliot Courtney wrote:
> +    pub fn push_init<E>(&mut self, init: impl Init<T, E>, flags: Flags) -> Result<(), E>
> +    where
> +        E: From<AllocError>,

This signature rejects impl Init<T, Infallible>, which is the reason why we have
e.g. Box::init() and Box::try_init() with different fallible signatures.

So, if we follow InPlaceInit, it'd be

	pub fn push_init<E>(&mut self, init: impl Init<T, E>, flags: Flags) -> Result<(), Error>
	where
	    Error: From<E>;

and

	pub fn try_push_init<E>(&mut self, init: impl Init<T, E>, flags: Flags) -> Result<(), E>
	where
	    E: From<AllocError>;

In theory we could also simplify it to

	pub fn push_init(&mut self, init: impl Init<T>, flags: Flags) -> Result<(), AllocError>

and

	pub fn try_push_init<E>(&mut self, init: impl Init<T, E>, flags: Flags) -> Result<(), E>
	where
	    E: From<AllocError>,

However, InPlaceInit actually achieves more with the init() and try_init()
distinction:

  What init() accepts, but try_init() does not accept:
    - impl Init<T, Infallible>
    - impl Init<T, E> where Error: From<E> but NOT E: From<AllocError>

  What try_init() accepts, but init() does not accept:
    - impl Init<T, E> where E: From<AllocError> but NOT Error: From<E>

So, with the simplification we'd technically lose out on the

	impl Init<T, E> where Error: From<E> but NOT E: From<AllocError>

case.

In any case, init() and try_init() seem a bit mixed up on their purpose
regarding fallibility and error type strategy, but in order to really cover all
cases I think it is necessary.