Update C-NEWTYPE-HIDE now impl Trait is shipped #178
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Strictly speaking, I think the change in this PR is correct, but I do have some concerns here. Namely, the way this is worded makes it seem like using impl Trait for these cases in public APIs is at least as good as using a newtype, but there are trade offs to consider here that I think might be worthwhile mentioning. Namely, with impl Trait, you are limited in what you can express. For example, returning an iterator that impls Debug or Clone or some combination of the other iterator extension traits can be problematic.
What I mean to say is that impl Trait as a return type is probably great for internal APIs and may even be appropriate for public APIs, but probably not in all cases.
src/future-proofing.md
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| [`impl Trait`]: https://github.com/rust-lang/rfcs/blob/master/text/1522-conservative-impl-trait.md | ||
| [impl-trait-2]: https://rust-lang-nursery.github.io/edition-guide/rust-2018/trait-system/impl-trait-for-returning-complex-types-with-ease.html | ||
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| ```rust | ||
| #![feature(conservative_impl_trait)] |
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I think you should remove this too?
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I remember your comments on Reddit about it, now. 😄 WDYT? |
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LGTM. cc @dtolnay |
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