Issue 2657 - Ambiguous duration instances #2670
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| @@ -9,12 +9,12 @@ package object instances { | |||
| object byte extends ByteInstances | |||
| object char extends CharInstances | |||
| object double extends DoubleInstances | |||
| object duration extends DurationInstances | |||
| object duration extends CoreDurationInstances with DurationInstances | |||
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I'm still trying to solve an issue here as importing both cats.instances.duration._ and cats.instances.finiteDuration._ explicitly prevents for the instance to be resolved. The scenario is when there's the need for kernel instances together with core's
object test {
import cats.instances.duration._
import cats.instances.finiteDuration._
implicitly[Order[Duration]]
implicitly[ContravariantShow[FiniteDuration]]
}
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This is why we don't have variance in type classes. I'd say in this case user have to use workarounds.
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I found a way to mitigate the problem. Now the only case that would fail is the below (see these test cases as an example).
test("fails") {
import cats.instances.duration._
import cats.instances.finiteDuration._
implicitly[ContravariantShow[Duration]] // fails compilation
implicitly[ContravariantShow[FiniteDuration]] // is inferred
}I couldn't find a way to remove also this drawback.
Codecov Report
@@ Coverage Diff @@
## master #2670 +/- ##
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+ Coverage 95.12% 95.13% +<.01%
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Files 364 365 +1
Lines 6707 6756 +49
Branches 285 300 +15
==========================================
+ Hits 6380 6427 +47
- Misses 327 329 +2
Continue to review full report at Codecov.
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I don't think I can do more here without breaking the BC. It's anyway a step forward compared to the current situation. If you agree, I would consider this PR complete. |
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This is to address #2657