Scalaでirof式。

Main.scala

object Main extends App {
  class irof[A](val condition: Boolean)(block: => A) {
    lazy val value = block

    def elof[B, C](elsePart: => B)(implicit e1: A <:< C, e2: B <:< C): C = {
      if (condition) value else elsePart
    }
  }

  object irof {
    def apply[A](condition: Boolean)(block: => A): irof[A] = {
      new irof(condition)(block)
    }

    implicit def toAnyVal[A <: AnyVal](irof: irof[A]): AnyVal = {
      irof.elof(())
    }

    implicit def toAny[A <: Any](irof: irof[A]): Any = {
      irof.elof(())
    }
  }

  val x: String = irof(true) {
    "foo"
  } elof {
    "bar"
  }

  val y: Any = irof(false) {
    "foo"
  } elof {
    1
  }

  val z: AnyVal = irof(false) {
    1
  }
}