add CoprodSubsetter for splitting coproducts #89
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core/src/coproduct.rs
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| /// # fn main() { | ||
| /// type I32F32 = Coprod!(i32, f32); | ||
| /// | ||
| /// // be aware that this particular example could be |
| /// assert_eq!(handle_anything(Anything::inject(4)), "...."); | ||
| /// # } | ||
| /// ``` | ||
| pub trait CoproductSubsetter<Targets, Indices>: Sized { |
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I wonder if this needs a separate trait or if it would be possible to simply do this as impls of CoproductUninjector with a label type?
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What do you mean by label type? In general I am fearful of having these be the same method (especially if it is entirely driven by type inference) because of the ambiguities created when you have a coproduct containing coproducts.
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Take a look at:
- https://docs.rs/frunk_core/0.0.23/frunk_core/hlist/trait.LiftInto.html
- https://docs.rs/frunk_core/0.0.23/frunk_core/hlist/trait.LiftFrom.html
- https://docs.rs/frunk_core/0.0.23/frunk_core/hlist/struct.Suffixed.html -- here's the index type.
Inference problems is a good point 👍
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@Centril That is the most criminally underdocumented and bizarre feature I have ever seen.
(Well, second most bizarre. The most bizarre feature I've seen are the impls of From and Into for tuples of the wrong size, sitting there right next to the impls for tuples of matching size)
The documentation of lift_from shows HLists being produced from single values.
- Why on earth is this same function also used to generate an HList from a prefix?
- Why a prefix and not a suffix? Why not an arbitrarily ordered subset?
- It shares my aforementioned concern about ambiguities.
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That is the most criminally underdocumented and bizarre feature I have ever seen.
Feel free to improve the documentation. The docs for LiftInto shows Hlists being produced from multiple values, but its out of sync with LiftFrom.
Why a prefix and not a suffix? Why not an arbitrarily ordered subset?
Prefixes are supported afaik.
Arbitrarily ordered subsets never crossed my mind; If you can improve on that, it would be nice.
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LGTM in general 👍 |
Part of #86.
Adds
CoprodSubsetterwith asubsetmethod to split a coproduct. The idea behind the name is that you are handling a subset of the types, leaving the rest for somebody else to handle.Added an example of using CoprodInjector for a match that is actually exhaustive. It didn't seem right for only
CoprodSubsetterto have such an example whenCoprodInjectorhas the word "exhaustive" right there in the headline.