sealed trait ImplicitNotFound[T] extends AnyRef
Extends the functionality of scala.annotation.implicitNotFound so that implicit-not-found error message is itself resolved using implicit search. This mechanism is used by Implicits.infer[T]:T* and macro engines that use it.
Example: we have a wrapper class Box[T]
and we want a custom error message when GenCodec[Box[T]]
for some type
T
is not found:
trait Box[T] object Box { implicit def boxCodec[T: GenCodec]: GenCodec[Box[T]] = ... @implicitNotFound("GenCodec for Box[$${T}] not found. This is most likely caused by lack of GenCodec[$${T}]") implicit def boxCodecNotFound[T]: ImplicitNotFound[GenCodec[Box[T]]] = ImplicitNotFound() }
It is also possible to compose error message for one type from error messages for other types. The example
above could reuse the implicit-not-found message for GenCodec[T]
when building the message for GenCodec[Box[T]]
:
@implicitNotFound("GenCodec for Box[$${T}] not found, because:\n#{forUnboxed}") implicit def boxCodecNotFound[T]( implicit forUnboxed: ImplicitNotFound[GenCodec[T]] ): ImplicitNotFound[GenCodec[Box[T]]] = ImplicitNotFound()
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