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package magnolia
import language.experimental.macros
import language.higherKinds
case class Thing(str: String) {
def access(path: String): Thing = Thing(s"$str.$path")
}
trait Extractor[T] { ext =>
def extract(src: Thing): T
def orElse[TS >: T, T2 <: TS](ext2: Extractor[T2]): Extractor[TS] = new Extractor[TS] {
def extract(src: Thing): TS = try ext.extract(src) catch {
case e: Exception => ext2.extract(src)
}
}
}
object Extractor extends Extractor_1 {
def apply[T](fn: Thing => T): Extractor[T] = new Extractor[T] {
def extract(source: Thing): T = fn(source)
}
implicit val intExtractor: Extractor[Int] = Extractor(_.str.length)
implicit val stringExtractor: Extractor[String] = Extractor(_.str)
implicit val doubleExtractor: Extractor[Double] = Extractor(_.str.length.toDouble)
implicit val dereferencer: Dereferencer[Extractor] { type Value = Thing } = new Dereferencer[Extractor] {
type Value = Thing
def dereference(value: Thing, param: String): Thing = value.access(param)
def delegate[T](extractor: Extractor[T], value: Thing): T = extractor.extract(value)
def combine[Supertype, Right <: Supertype](left: Extractor[_ <: Supertype],
right: Extractor[Right]): Extractor[Supertype] = left.orElse(right)
def construct[T](body: Thing => T): Extractor[T] = new Extractor[T] {
def extract(source: Thing): T = body(source)
}
}
}
trait Extractor_1 extends Extractor_2 {
implicit def listExtractor[T: Extractor]: Extractor[List[T]] = new Extractor[List[T]] {
def extract(source: Thing): List[T] = List(implicitly[Extractor[T]].extract(source))
}
}
trait Extractor_2 {
implicit def generic[T]: Extractor[T] = macro Macros.magnolia[T, Extractor[_]]
}
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