How to find if a Scala String is parseable as a Double or not?

Question

Suppose that I have a string in scala and I want to try to parse a double out of it.

I know that, I can just call toDouble and then catch the java num

Answer 1

scala> import scala.util.Try
import scala.util.Try

scala> def parseDouble(s: String): Option[Double] = Try { s.toDouble }.toOption
parseDouble: (s: String)Option[Double]

scala> parseDouble("3.14")
res0: Option[Double] = Some(3.14)

scala> parseDouble("hello")
res1: Option[Double] = None

Answer 2

Unfortunately, this isn't in the standard library. Here's what I use:

class SafeParsePrimitive(s: String) {
  private def nfe[T](t: => T) = {
    try { Some(t) }
    catch { case nfe: NumberFormatException => None }
  }
  def booleanOption = s.toLowerCase match {
    case "yes" | "true" => Some(true)
    case "no" | "false" => Some(false)
    case _ => None
  }
  def byteOption = nfe(s.toByte)
  def doubleOption = nfe(s.toDouble)
  def floatOption = nfe(s.toFloat)
  def hexOption = nfe(java.lang.Integer.valueOf(s,16))
  def hexLongOption = nfe(java.lang.Long.valueOf(s,16))
  def intOption = nfe(s.toInt)
  def longOption = nfe(s.toLong)
  def shortOption = nfe(s.toShort)
}
implicit def string_parses_safely(s: String) = new SafeParsePrimitive(s)