It is an error to incompatibly override an equivalence constraint. #6
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hadronized
reviewed
Apr 13, 2017
| trait IntIterator = Iterator<Item=i32>; | ||
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| fn quux1<T: SharableIterator<Item=f64>>(...) { ... } // ok | ||
| fn quux2<T: IntIterator<Item=i32>>(...) { ... } // ok (perhaps subject to lint warning) |
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I think this shoudn’t be authorized?
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I am happy either way.
Originally I was going to list it as disallowed, as you suggest.
But then I worried that might not be consistent with other design choices. E.g. one can add where clauses that are already implied by pre-existing constraints, right? So should it be an error to add a redundant equivalence constraint?
Maybe best (or at least easiest in terms of getting the RFC merged) to take out the fn quux2 example, and then make a new Unresolved Question for this case?
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Well, I think you’re right about the consistency. Others construct follow such a pattern. I’ll merge it then.
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This is another detail that I had wanted spelled out explicit in the RFC; see rust-lang#1733 (comment)
(I am assuming that we want it to be legal to put in redundant constraints; that's the case I wrote that we might issue a lint warning for in the text I'm adding here. But maybe this is actually an unresolved question?)