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Path dependent types with an implicit prefix. We can infer the singleton type prefix of a path dependent type and then implicitly summon the unique value of that singleton type.
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| Welcome to Scala version 2.10.2 (Java HotSpot(TM) 64-Bit Server VM, Java 1.7.0_21). | |
| Type in expressions to have them evaluated. | |
| Type :help for more information. | |
| scala> class Prefix { class Dep { type P = Prefix.this.type } } | |
| defined class Prefix | |
| scala> val (p1, p2) = (new Prefix, new Prefix) | |
| p1: Prefix = Prefix@2212c414 | |
| p2: Prefix = Prefix@7e070e85 | |
| scala> val (d1, d2) = (new p1.Dep, new p2.Dep) | |
| d1: p1.Dep = Prefix$Dep@798ab9b2 | |
| d2: p2.Dep = Prefix$Dep@2a59375 | |
| scala> def prefix[P <: Prefix](dep: P#Dep)(implicit p: dep.P): P = p // Infer singleton type P, then summon it. | |
| prefix: [P <: Prefix](dep: P#Dep)(implicit p: dep.P)P | |
| scala> implicit val ip1 = p1 | |
| ip1: Prefix = Prefix@2212c414 | |
| scala> implicit val ip1: p1.type = p1 | |
| ip1: p1.type = Prefix@2212c414 | |
| scala> implicit val ip2: p2.type = p2 | |
| ip2: p2.type = Prefix@7e070e85 | |
| scala> prefix(d1) | |
| res0: Prefix = Prefix@2212c414 | |
| scala> prefix(d2) | |
| res1: Prefix = Prefix@7e070e85 |
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