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Allow opting out of the fallback OptJsonWriter 

Simply

    import OptJsonWriter.OptOut._

And you'll get the implicit lift, but not the implicit fallback.

You get an ambiguous compile error like this:

    [error] /d/sbt-util/internal/util-collection/src/main/scala/sbt/util/OptJsonWriter.scala:28: ambiguous implicit values:
    [error]  both method conflictingFallback1 in trait OptOut0 of type [A]=> sbt.util.NoJsonWriter[A]
    [error]  and method conflictingFallback2 in trait OptOut0 of type [A]=> sbt.util.NoJsonWriter[A]
    [error]  match expected type sbt.util.OptJsonWriter[Foo]
    [error]     val x = implicitly[OptJsonWriter[Foo]]
    [error]                       ^
This commit is contained in:
Dale Wijnand 2017-03-21 17:12:10 +00:00
parent 9cfa17d09e
commit 0713e31cea
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8
internal/util-collection/src/main/scala/sbt/util/OptJsonWriter.scala
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@ -11,4 +11,12 @@ trait OptJsonWriter0 {
}
object OptJsonWriter extends OptJsonWriter0 {
implicit def lift[A](implicit z: JsonWriter[A]): SomeJsonWriter[A] = SomeJsonWriter(z)
trait OptOut0 {
implicit def conflictingFallback1[A]: NoJsonWriter[A] = NoJsonWriter()
implicit def conflictingFallback2[A]: NoJsonWriter[A] = NoJsonWriter()
}
object OptOut extends OptOut0 {
implicit def lift[A](implicit z: JsonWriter[A]): SomeJsonWriter[A] = SomeJsonWriter(z)
}
}