生成随机大小的Scala列表

Question

I am creating a scala json using :

lazy val genDefaultValue: Gen[List[JsonPatch]] = {
listOf(
  genJson("/primary", true),
  genJson("/secondary", true),
  genJson("/fallback", true)
)
}

This creates only a random json with one of the item. I am unable to create a list of random size using above 3 list elements. ListSize can be anything between 1 to 3.

genJson is an internal function which creates a Json when passed a path, Gen[T] for expected type.

Answer 1

One option is as follows:

1. Reorder the list with Random.shuffle() (if you want the order to differ each time).
2. Call .take(x) on the (optionally shuffled) list, where x is a random value between 1 and 3.

Answer 2

Assuming you're using ScalaCheck and genJson returns an instance of Gen[JsonPatch] , the following code defines a generator for lists of JsonPatch instances:

lazy val genDefaultvalue =
   Gen.listOf(Gen.oneOf(genJson("/primary", true),
                        genJson("/secondary", true),
                        genJson("/fallback", true)))