Scala: single abstract methods without a parameter

Question

With SAM types, we can have:

trait Sam {
  def foo(i: Int): String
}

val sam : Sam = _.toString

What if my abstract method doesn't have a parameter?

Answer 1

You can use a lambda with an empty argument list like this:

trait Sam {
  def foo(): String
}

val sam : Sam = () => "hello"

You can not use _ notation because there's no way to define a zero-argument function with _.

This won't work if foo is defined as def foo: String instead (i.e. if it doesn't have a parameter list) because SAM-conversion only applies if the single method has exactly one parameter list.