Subtle scala quirk with implicit conversions

boom.scala

@ "42".toInt
res0: Int = 42

@ implicit object Foo extends Function1[String, Int] {
    def apply(s: String) = s.toInt
  }
defined object Foo

@ "42”.toInt
// BOOM (infinite recursion)

Explanation: calling toInt (not defined on String) triggers an implicit lookup, which usually hits the toInt method defined on StringLike

Too bad that toInt is defined also on Int and we're providing an implicit function from String to Int, which has the precedence (it's "closer" in the scope) and uses toInt.

Result (after implicit expansion):

implicit object Foo extends Function1[String, Int] {
  def apply(s: String) = Foo.apply(s).toInt // <-- infinite recursion
}