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Diffstat (limited to 'src/library')
-rw-r--r-- | src/library/scala/annotation/implicitAmbiguous.scala | 34 |
1 files changed, 34 insertions, 0 deletions
diff --git a/src/library/scala/annotation/implicitAmbiguous.scala b/src/library/scala/annotation/implicitAmbiguous.scala new file mode 100644 index 0000000000..46eab9ae8f --- /dev/null +++ b/src/library/scala/annotation/implicitAmbiguous.scala @@ -0,0 +1,34 @@ +package scala.annotation + +import scala.annotation.meta._ + +/** + * To customize the error message that's emitted when an implicit of type + * C[T1,..., TN] is found more than once, annotate the class C + * with @implicitAmbiguous. Assuming C has type parameters X1,..., XN, the + * error message will be the result of replacing all occurrences of ${Xi} in + * the string msg with the string representation of the corresponding type + * argument Ti. * + * + * If more than one @implicitAmbiguous annotation is collected, the compiler is + * free to pick any of them to display. + * + * Nice errors can direct users to fix imports or even tell them why code + * intentionally doesn't compile. + * + * {{{ + * trait =!=[C, D] + * + * implicit def neq[E, F] : E =!= F = null + * + * @annotation.implicitAmbiguous("Could not prove ${J} =!= ${J}") + * implicit def neqAmbig1[G, H, J] : J =!= J = null + * implicit def neqAmbig2[I] : I =!= I = null + * + * implicitly[Int =!= Int] + * }}} + * + * @author Brian McKenna + * @since 2.12.0 + */ +final class implicitAmbiguous(msg: String) extends scala.annotation.StaticAnnotation {} |