Created
July 26, 2017 13:59
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| import shapeless._ | |
| def abc0[M[_]] = ??? | |
| def abc1[M[+_]] = ??? | |
| def abc2[M[-_]] = ??? | |
| //this one should accept an arbitrary invariant M | |
| def abc3[M[_] <: Set[_]] = ??? | |
| type Predicate[-a] = a => Boolean | |
| //M[_] works for all | |
| abc0[Predicate] | |
| abc0[List] | |
| abc0[Set] | |
| //M[+_] works for covariant types | |
| illTyped("""abc1[Predicate]""") | |
| abc1[List] | |
| illTyped("""abc1[Set]""") | |
| //M[-_] works for contravariant types | |
| abc2[Predicate] | |
| illTyped("""abc2[List]""") | |
| illTyped("""abc2[Set]""") | |
| //this should happen | |
| illTyped("""abc3[List]""") | |
| illTyped("""abc3[Predicate]""") | |
| abc3[Set] |
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