gistfile1.txt

Welcome to Scala 2.12.0-M5 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_45).
Type in expressions for evaluation. Or try :help.

scala> case class Foo(x: Int)
defined class Foo

scala> implicit def foo: Foo = Foo(1)
foo: Foo

scala> implicitly[Foo]
res0: Foo = Foo(1)

scala> implicit def foo: Foo = Foo(2)
foo: Foo

scala> implicitly[Foo]
res1: Foo = Foo(2)

scala> implicit def foo2: Foo = Foo(3)
foo2: Foo

scala> implicitly[Foo]
<console>:18: error: ambiguous implicit values:
 both method foo of type => Foo
 and method foo2 of type => Foo
 match expected type Foo
       implicitly[Foo]
                 ^