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gadthelp
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| sealed trait Scenario[A, B] | |
| object Scenario { | |
| // later pattern matching let's me do GADT stuff in pattern matches fine | |
| case object A extends Scenario[AA, AA1] | |
| case object B extends Scenario[BB, BB1] | |
| // but how to get into this domain from the outside is the problem...(this doesn't compile obviously) | |
| def from[A, B](s: String): Scenario[A, B] = s match { | |
| case "a" => A | |
| case "b" => B | |
| } | |
| } | |
| // later usage using the GADT in a pattern match | |
| def from[A, B](scenario: Scenario[A, B]): Box[A, B] = scenario match { | |
| case A => constantA // returns some Box[AA, AA1] | |
| case B => constantB // returns some Box[BB, BB1] | |
| } | |
| // later later usage | |
| // relies on the answer of Box[A, B] to lookup implicits for A, B. | |
| // I can use an existential type to parse the string and return Scenario[_,_] later | |
| // but then I lose the fact it's AA, AA1 or BB, BB1 later | |
| // and a bunch of implicit lookups fail because it can't find implicits for | |
| // _$1, and _$2 |
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