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class MyFunc[-A, +B] extends (A => B) { def apply(x: A): B = ??? }
class MyCollection[A] {
def map[B](f: MyFunc[A, B]): MyCollection[B] = new MyCollection[B]
}
class OtherFunc[-A, +B] {}
object Test {
implicit def functionToMyFunc[A, B](f: A => B): MyFunc[A, B] = new MyFunc
implicit def otherFuncToMyFunc[A, B](f: OtherFunc[A, B]): MyFunc[A, B] = new MyFunc
def main(args: Array[String]) {
val col = new MyCollection[Int]
// Doesn't compile: error: missing parameter type for expanded function ((x$1) => x$1.toString)
println(col.map(_.toString))
// Doesn't compile: error: missing parameter type
println(col.map(x => x.toString))
// Does compile
println(col.map((x: Int) => x.toString))
// Does compile (even though type params of OtherFunc not given)
println(col.map(new OtherFunc))
}
}
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