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

Scalaz provides an extension method parseDouble on Strings, which gives a value of type Validation[NumberFormatException, Double].

scala> "34.5".parseDouble
res34: scalaz.Validation[NumberFormatException,Double] = Success(34.5)

scala> "34.bad".parseDouble
res35: scalaz.Validation[NumberFormatException,Double] = Failure(java.lang.NumberFormatException: For input string: "34.bad")

You can convert it to Option if so required.

scala> "34.bad".parseDouble.toOption
res36: Option[Double] = None