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Tagger / Untagger
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| /* | |
| Based on @milessabin's https://gist.github.com/milessabin/89c9b47a91017973a35f | |
| Note the swap: T for Tag and U for Untagged type | |
| */ | |
| type Tag[U, T] = { | |
| type Tag = T | |
| type Untagged = U | |
| } | |
| type @@[U, T] = U with Tag[U, T] | |
| implicit class Tagger[U](untagged: U) { | |
| def tagged[T]: U @@ T = untagged.asInstanceOf[U @@ T] | |
| } | |
| implicit class Untagger[U, T](tagged: @@[U,T]) { | |
| def untag : U = tagged | |
| } | |
| trait New | |
| trait Persisted | |
| case class Foo(name:String) | |
| val foo = Foo("abc") | |
| val taggedFoo = foo.tagged[New] | |
| // taggedFoo: @@[Foo,New] = Foo(abc) | |
| val untaggedFoo = taggedFoo.untag | |
| // untaggedFoo: this.Untagged = Foo(abc) | |
| val untaggedFooOneLiner = foo.tagged[Persisted].untag | |
| // untaggedFooOneLiner: Foo = Foo(abc) |
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| /* | |
| When type Untagged is commented out, it's impossible to untag, although type U is known | |
| */ | |
| type Tag[U, T] = { | |
| type Tag = T | |
| // type Untagged = U | |
| } | |
| type @@[U, T] = U with Tag[U, T] | |
| implicit class Tagger[U](untagged: U) { | |
| def tagged[T]: U @@ T = untagged.asInstanceOf[U @@ T] | |
| } | |
| implicit class Untagger[U, T](tagged: @@[U,T]) { | |
| def untag : U = tagged | |
| } | |
| trait New | |
| trait Persisted | |
| case class Foo(name:String) | |
| val foo = Foo("abc") | |
| val taggedFoo = foo.tagged[New] | |
| // taggedFoo: @@[Foo,New] = Foo(abc) | |
| val untaggedFoo = taggedFoo.untag | |
| //untaggedFoo: @@[Foo,New] = Foo(abc) | |
| val untaggedFooOneLiner = foo.tagged[Persisted].untag | |
| // untaggedFooOneLiner: Foo = Foo(abc) |
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