Inconsistent behavior of the compiler for ambiguous implicit views implemented as vals or defs #6316
Description
When defining a ambiguous implicit view, the compiler will complain for an implicit def, but not for an implicit val:
scala> implicit val impl: String => Int = (s: String) => s.toInt
impl: String => Int = <function1>
scala> "2" - 1
java.lang.StackOverflowError
at $anonfun$1.apply(<console>:9)
scala> implicit def stringToInt(s: String): Int = s.toInt
<console>:7: error: type mismatch;
found : s.type (with underlying type String)
required: ?{def toInt: ?}
possible cause: missing arguments for method or constructor
Note that implicit conversions are not applicable because they are ambiguous:
both method augmentString in object Predef of type (x: String)scala.collection.immutable.StringOps
and method stringToInt of type (s: String)Int
are possible conversion functions from s.type to ?{def toInt: ?}
implicit def stringToInt(s: String): Int = s.toInt
Further the implicit view is not ambiguous if the type annotation on the val or def is omitted:
scala> implicit val impl = (s: String) => s.toInt
impl: String => Int = <function1>
scala> "2" - 1
res0: Int = 1scala> implicit def stringToInt(s: String) = s.toInt
stringToInt: (s: String)Int
scala> "2" - 1
res0: Int = 1