Improve opaque types

Language Design
12

You can abstract this stuff away pretty well:

scala> trait NewType[A]:
     |   opaque type Type = A
     |   def apply(a: A): Type = a
     |   extension (a: Type) def value: A = a
     | end NewType
// defined trait NewType

scala> object Bar extends NewType[String]
// defined object Bar

scala> val bar = Bar("foo")                                                
val bar: Bar.Type = foo

scala> bar.value
val res6: String = foo

Of course it’s not 100% the same API and has some drawbacks as discussed in the other thread (mainly with boxing of primitives).

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