Never patterns, exhaustive matching, and uninhabited types in Rust

Re:Never patterns, exhaustive matching, and uninhabited type... by ChrisSD on Saturday August 18, 2018 @08:48AM (#17788219)

I've used `enum Void { }` as a placeholder for opaque FFI managed types that I pass between APIs but never inspect myself. Like Windows handles (`*const Void`) or data structures that are queried using an API rather than directly.

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Re:Never patterns, exhaustive matching, and uninhabited type... by nalllar on Saturday August 18, 2018 @09:51AM (#17788448)

enum Void shouldn't be used for opaque types.

See these: https://internals.rust-lang.org/t/recent-change-to-make-exha... https://github.com/rust-lang-nursery/nomicon/issues/29 https://github.com/briansmith/ring/issues/416

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Re:Never patterns, exhaustive matching, and uninhabited type... by ChrisSD on Saturday August 18, 2018 @09:54AM (#17788464)

Oh wow, I didn't know this. At one time at least it was recommended, which was why I did it.

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Re:Never patterns, exhaustive matching, and uninhabited type... by bjz_ on Saturday August 18, 2018 @10:31AM (#17788610)

Yeah, IIRC many years ago I added it in a document as a pattern for C APIs (I can't remember where though). Either other people were doing the same thing, or were influenced by that. Anyway, you should use `*const libc::void` these days! Sorry for the confusion.

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