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package cc.spray.json
package lenses
/**
* This typeclass with its implicit instances decides how two containers should be joined.
*
* Supported containers are
*
* * `Id` for scalar values
* * `Option` for optional values
* * `Seq` for a vector of values
*
* Those container types form an ordering from most specific to most abstract:
*
* * `Id` contains always one value
* * `Option` contains always zero or one value
* * `Seq` can contain any number of values
*
* The rule to determine what the result type of joining two container types is that the result
* is as generic as the more generic of both of the input types.
*
* The implicit definitions in the companion object of join form evidence for this ordering.
*/
trait Join[M1[_], M2[_], R[_]] {
def get(outer: Ops[M1], inner: Ops[M2]): Ops[R]
}
object Join {
def apply[M1[_], M2[_], R[_]](f: ((Ops[M1], Ops[M2])) => Ops[R]): Join[M1, M2, R] = new Join[M1, M2, R] {
def get(outer: Ops[M1], inner: Ops[M2]): Ops[R] = f(outer, inner)
}
implicit def joinWithSeq[M2[_]]: Join[Seq, M2, Seq] = Join(_._1)
implicit def joinWithScalar[M2[_]]: Join[Id, M2, M2] = Join(_._2)
implicit def joinWithOptionWithId: Join[Option, Id, Option] = Join(_._1)
implicit def joinOptionWithOption: Join[Option, Option, Option] = Join(_._1)
implicit def joinOptionWithSeq: Join[Option, Seq, Seq] = Join(_._2)
}
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