What is the syntax for Single Abstract Method with generic types in a trait

Question

Say I define a class with ordering as below:

case class C(i: Int)

implicit def ordering[A <: C]: Ordering[A] = new Ordering[A] {
    def compare(c1: A, c2: A): Int = c1.i.compareTo(c2.i)
}

I get the following info from the compiler:

Convert expression to Single Abstract Method less... (Ctrl+F1) Inspection info: Checks if an expression can be converted to SAM (Single Abstract Method). Before: new Thread(new Runnable { override def run() = println() }
After: new Thread(() => println())

But it is not obvious to me what the correct syntax in this case is? I have tried the code below but it does not compile:

implicit def ordering[A <: C]: Ordering[A] = new Ordering[A]((c1: A, c2: A) => c1.i.compareTo(c2.i))

Answer 1

The correct syntax is:

 implicit def ordering[A <: C]: Ordering[A] = (c1: A, c2: A) => c1.i.compareTo(c2.i)

Single Abstract Methods are used when you create an instance of a trait with one and only one method.

SAM comes from java8, and were introduced in scala 2.12: