Clarify the relationships between various kinds of structs and variants #1506
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| As a basic struct, a unit struct can participate in struct expressions `US{}`, including FRU | ||
| `US{..s}` and in struct patterns `US{}`/`US{..}`. In both cases the path `US` of the expression | ||
| or pattern is looked up in the type namespace. |
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A unit struct/variant pattern is a struct/variant pattern, not a constant pattern, and therefore is exhaustive.
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There's a "Note 1" below (I could expand it though).
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I really like these ideas. If they're not taken up by Rust, I may steal them for my own language :) |
Mention type aliases
Mention differences between unit structs / tuple struct constructors and `const` / `fn` items.
Add more use cases for `TS{0: expr}`/`TS{0: pat}`
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| Fields of a braced struct can be accessed with dot syntax `s.field1`. | ||
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| Note: struct *variants* are currently defined in the value namespace in addition to type namespace, | ||
| there are no particular reasons for this and this is probably temporary. |
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I guess this is because regular variants are in both namespaces and braced variants are a mistake. However, if we one day get named fields for functions, then I guess we could use struct names as ctor functions, so it might be useful. Too bad that ship has sailed for regular structs.
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Implementation: rust-lang/rust#35138 |
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Note that everything the implementation does (modulo tests and feature gates) is removing non-fatal errors and accepting a new grammar production in the parser, i.e. the RFC only legitimizes things that already work internally. |
| function calls, but the compiler reserves the right to make observable improvements to them based | ||
| on the additional knowledge, that `TS` is a constructor. | ||
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| Note 1: the automatically assigned field names are quite interesting, they are not identifiers |
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This note doesn't appear to be used in the above section.
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Hear ye, hear ye! This RFC is now entering final comment period. In the most recent meeting, @nrc and I (the only two in attendance) both felt inclined to accept (though no final decision has been reached). In general, the feeling is that this RFC is not needed in any strict sense, though enabling |
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I think making the model easier to understand and more consistent (and without breaking anything) is worth it in its own right. Making macros simpler is pretty awesome too. The only worry is that there is some future feature that would need this syntax. On the other hand, this RFC makes a pretty clear case that such new syntax would be confusing and non intuitive. I'm 👍 |
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Also, making TupleStruct just shorthand for NamedStruct but with numeric names makes a lot of sense imo. Not having to do |
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I'm not sure I totally understand the "pattern matching a function" definition though. You can't pattern match to a function, so it is really confusing. I would change that description to something more accurate with how things actually work |
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I think this is a great change. I agree it's not necessary, but it also seems "good", without much, if any, downside. |
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I'm very much in favor as well. This is exactly the mental model I want, and I'd love to get rid of the various pedantic restrictions we have today. |
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Huzzah! The @rust-lang/lang team has decided to accept this RFC. |
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Tracking issue: rust-lang/rust#35626 If you'd like to keep following the development of this feature, please subscribe to that issue, thanks! :) |
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Hello, sorry to bother you with this, but the rendered proposal link is broken, I think it should be: https://github.com/rust-lang/rfcs/blob/master/text/1506-adt-kinds.md [From the mod: Fixed now.] |
Provide a simple model describing three kinds of structs and variants and their relationships + some small language extensions following from this model.
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cc rust-lang/rust#31757 (comment)