scala,implicit-conversion , Type to impose required constrains on a double

## Question:

Tag: scala,implicit-conversion

I would like to have a run time check on a Double, without having to scatter the check all over my code. I thought that defining an `implicit class` would do the job, something on the line:

``````  implicit class Probability(val x: Double) {
require(x >= 0.0 && x <= 1.0, "Probs are defined btw 0.0 and 1.0")
}
``````

The missing part, is then to tell Scala to treat Probability as a `Double` any time after it's construction. For this I suppose it is necessary to require a double side conversion.

``````object Foo {

implicit class Probability(val x: Double) {
require(x >= 0.0 && x <= 1.0, "Probs are defined btw 0.0 and 1.0")
}

implicit def asDouble(e: Probability): Double = e.x

implicit def asProb(d: Double): Probability = new Probability(d)

def max_(s: Seq[Double]): Double = {
s.max
}

def max(s: Seq[Probability]): Double = {
s.max
}
}

val r1 = Foo.max_(List(2.0, 3.0, 5.0))
val r2 = Foo.max(List[Probability]=(2.0, 3.0, 5.0))
``````

EDIT

This might have done the trick. Not sure what happens under the hood.

``````trait RangeBound
type Probability = Double with RangeBound
implicit def makeProb(p: Double): Probability = {
assert (p >= 0.0 && p <= 1.0)
p.asInstanceOf[Probability]
}

val p = List[Probability](0.1, 0.3, 0.2)
val r = p filter (_ > 0.1)
``````

Because this does not work:

``````trait RangeBound
type Probability = Double with RangeBound
implicit def makeProb(p: Double): Probability = {
assert (p >= 0.0 && p <= 1.0)
p.asInstanceOf[Probability]
}

val p = List[Probability](0.1, 0.3, 0.2)
val r2 = p.max
``````

with the error:

``````Error:(10, 18) No implicit Ordering defined for Double with A\$A288.this.RangeBound.
lazy val r2 = p.max;}
^
``````

This enabled basic run time checks:

``````trait RangeBound
type Probability = Double with RangeBound

implicit def makeProb(p: Double): Probability = {
assert (p >= 0.0 && p <= 1.0)
p.asInstanceOf[Probability]
}

implicit val probabilityOrdering = Ordering.Double.asInstanceOf[Ordering[Probability]]
``````

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