Add bounds to CoproductInstances methods #41
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This restricts the implementation of sums to subtypes, but this implementation is already restricted by `Mirror.Sum` which is used in `ErasedCoproductInstances`. This allows us to implement coproduct folds that return the upper bound as a result, e.g. that would replace `traverse`.
| @@ -102,7 +102,7 @@ class InstancesTests { | |||
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| val expected = "f 326" | |||
| val actual = otherInst.fold[String](f) { | |||
| [t] => (f: AnotherTypeClass[t], t: t) => "f " + f.method(t) | |||
| [t <: Few[Int]] => (f: AnotherTypeClass[t], t: t) => "f " + f.method(t) | |||
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I don't know why this was necessary - the poly function without a bound should be a subtype
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This seems to be in direct conflict with an attempt to fix #21. Suppose we, or some other library, or an application, provided |
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Unions are still super types. Where it could break down is e.g. with a nested |
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Maybe the alternative is to provide an |
I'm not keen on that, because we want the erased operation to be just a cast.
This is right of course, so I don't actually have any objections here. |
This restricts the implementation of sums to subtypes,
but this implementation is already restricted by
Mirror.Sumwhich is used in
ErasedCoproductInstances.This allows us to implement coproduct folds that return the
upper bound as a result, e.g. that would replace
traverse.