Trait object syntax + trailing plus #255
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src/types.md
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| of auto traits followed optionally by a lifetime bound all separated by and | ||
| optionally terminated by `+`. For example, given a trait `Trait`, the following | ||
| are all trait objects: `Trait`, `Trait + Send`, `Trait + Send + Sync`, | ||
| `Trait + 'static`, `Trait + Send + 'static`, `Trait +`. |
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'static + Send + Trait also works.
In general, trait objects have exactly the same syntax as bounds after T in fn f<T: BOUNDS>() { ... }, it would be great to unify them in the reference as well.
Trait objects just have some additional semantic restrictions (n(lifetimes) <=1, n(non-auto-traits) <=1).
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'static + Send + Trait explicitly doesn't work giving me error[E0225]: only auto traits can be used as additional traits in a trait object. 'static + Trait does work.
Generic bounds don't seem to be in the reference at all right now. 🙁
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I'm working on adding some documentation for them soon.
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Added lifetimes to the grammar and said they are written the same as trait bounds. @matthewjasper Feel free to move the grammar over to describing type bounds when you get to it, and then change the grammar for trait objects to just be "TypeBounds". |
src/types.md
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| `Trait + Send + 'static`. | ||
| Trait objects are written the same as trait bounds with the exception that all | ||
| traits except the first trait must be auto traits and there may not be more than | ||
| one lifetime. For example, given a trait `Trait`, the following |
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and ? bounds ("opt-out bounds"?) can't be used.
src/types.md
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| example, given a trait `Trait`, the following are all trait objects: `Trait`, | ||
| `Trait + Send`, `Trait + Send + Sync`, `Trait + 'static`, | ||
| `Trait + Send + 'static`. | ||
| Trait objects are written the same as trait bounds with the exception that all |
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I think this would be clearer as separate sentences instead of "with the exception that".
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I've addressed the two points. |
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Thanks! |
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