Tracking issue for array::try_map

Feature gate: #![feature(array_try_map)]

This is a tracking issue for

Public API

https://doc.rust-lang.org/nightly/std/primitive.array.html#method.try_map

impl<T, const N: usize> [T; N] {
    pub fn try_map<F, R>(
        self,
        f: F
    ) -> <<R as Try>::Residual as Residual<[<R as Try>::Output; N]>>::TryType
    where
        F: FnMut(T) -> R,
        R: Try,
        <R as Try>::Residual: Residual<[<R as Try>::Output; N]>;
}

Steps / History

Implementation: ~~array::try_map #79713~~ Make array::{try_from_fn, try_map} and Iterator::try_find generic over Try #91286
Decide on just-Result, vs potentially supporting Option and other Try types Decide on generic-ness of functions like Iterator::try_find and array::try_map #85115
Final commenting period (FCP)
Stabilization PR

Unresolved Questions

None yet.

Not sure if this change is still active, but I've stumbled upon a use case where a broader version of this for iterators in general, rather than strictly for arrays, would be useful. Is that something worth considering?

I'm totally new to both Rust contributions & open source in general, so I'm not sure if the idea of a general try_map is worth considering/pursuing, but I just thought I'd throw the idea out there since I thought it would be useful. Appreciate any feedback & insights!

(And, if it gets to that point, I'd be interested in taking a stab at implementing it. Would love to make a contribution to Rust, no matter how small!)

@arthurlafrance It'd suggest starting a conversation on IRLO about it. Or you can send a PR if it'd be easier to just write the code.

This change is still open, but is for tracking this specific change, not a good place to discuss an additional possible API.

+1 for this one, it's the only way I found to run a fallible .map() without collecting to a Vec, and still use Try afterward, which leads to a concise and straightforward code.

Not sure if this change is still active, but I've stumbled upon a use case where a broader version of this for iterators in general, rather than strictly for arrays, would be useful.

I guess that's what iter.collect::<Result<_>>() and the unstable iter.try_collect() are intended for.

Is there anything blocking stabilization?

Note that this, like array::try_from_fn and Iterator::try_find and similar, depends on the Residual trait mechanism for mapping from Foo<A> to Foo<[A; N]>, which is not used in any stable functions right now, so stabilization here is a bigger question than just the specific function in question.

See #94119 (comment) where array::from_fn was accepted but array::try_from_fn wasn't accepted due to this.

I believe #91285 is the tracking issue for stabilizing Residual

Right, stabilizing try_map doesn't require stabilizing Residual itself, but it does expose it, which is itself a commitment to have something like it forever.

Thank you for the replies! As far as I understood, there is a consensus that exposing Try trait in stable APIs is ok (e.g. Iterator::try_fold is stable) while exposing Residual is not, even though they both belong to try_trait_v2.

In this case, is it possible to rewrite the current implementation to only use Result/Option, stabilize it and revert back to a more general case when Residual trait gets stabilized?

I don't think it's possible to rewrite with Result/Option without changing the number or meaning of try_maps generic parameters in a way that won't be backward compatible with the revert.

Rollup merge of rust-lang#118087 - GrigorenkoPV:refcell_try_map, r=Ma…

Unrolled build for #118087

Rollup merge of #118087 - GrigorenkoPV:refcell_try_map, r=Mark-Simula…

Rollup merge of rust-lang#118087 - GrigorenkoPV:refcell_try_map, r=Ma…

Rollup merge of #118087 - GrigorenkoPV:refcell_try_map, r=Mark-Simula…

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Tracking issue for `array::try_map` #79711

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Tracking issue for array::try_map #79711

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Public API

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a-lafrance commented on Nov 12, 2021

scottmcm commented on Dec 4, 2021

marcospb19 commented on Aug 20, 2023

SmnTin commented on Aug 27, 2023

scottmcm commented on Aug 28, 2023

tarcieri commented on Aug 28, 2023

scottmcm commented on Aug 28, 2023

SmnTin commented on Aug 29, 2023

SmnTin commented on Aug 29, 2023

eopb commented on Sep 19, 2023

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Tracking issue for `array::try_map` #79711