Cats typeclass priority hierarchy #647
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RustedBones
changed the title
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| class ScopeTest extends FunSuite { | ||
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| test("auto implicit will give most powerful abstraction") { |
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This is how scala solves implicit conflicts.
In our case we could have only defined those as the other implicits methods can't be called explicitly due to the shapeless LowPriority
| // use shapeless.LowPriority so the | ||
| // provided cats type classes are always preferred | ||
| // triggers derivation as last resort |
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we unfortunately have to keep shapeless.LowPriority to avoid conflicts with implicits provided in cats._
| // triggers derivation as last resort | ||
| package object auto extends LowPriority0Implicits | ||
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| trait LowPriority0Implicits extends LowPriority2Implicits { |
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I wonder how this worked before the fix. Wrong type class was picked up by compiler?
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I think the shapeless.LowPriority got our back and was giving one of the implicit depending on the resolution.
| implicitly[Group[Numbers]] | ||
| implicitly[CommutativeGroup[Numbers]] | ||
| implicitly[Show[Numbers]] | ||
| val s: Show[Numbers] = implicitly |
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is this a matter of style?
upd: Oh OK. I see it below
Respect cats typeclass hierarchy for implicit resolution as defined here
In practice, this was not creating any issue due to the usage of
shapeless.LowPrioritybut intelliJ linter was showing conflicts in resolution.This fixes the lint errors and with scala 3, we'll have to define implicit priority properly anyway.
Tests were not run on the desired instance