Construct a function to return the default value of any type:

import scala.compiletime.uninitialized
def default[T]:T = {
    class Default[T] { var value:T = uninitialized }

    Default[T].value
}
default[Double]   // Double = 0.0
default[Boolean]  // Boolean = false
default[Int]      // Int = 0

This pattern match does not work (why?):

def matchType[T]():T = {
    default[T] match {
        case d:Double => d
        case i:Int => i
        case b:Boolean => b
    }
}

matchType[Double]()

scala.MatchError: null
  ammonite.$sess.cmd37$.matchType(cmd37.sc:5)
  ammonite.$sess.cmd37$.<clinit>(cmd37.sc:9)

Why is the pattern match failing?

In both cases (top case: using default[Double] and bottom case: using matchTypeDouble) everything is known at compile time.

Motivation for this question: convert a string to a type where you specify the type T, then use pattern match to handle different functionality at runtime. e.g. fromStringToDouble would pattern match on the Double (using default[Double]) and use functionality at runtime to convert “3.14” to 3.14:Double using e.g. toString