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

There's nothing like this not only in Scala, but even in basic Java.

Here's a piece code that does it without exceptions, though:

def parseDouble(s: String)(implicit nf: NumberFormat) = {
    val pp = new ParsePosition(0)
    val d = nf.parse(s, pp)
    if (pp.getErrorIndex == -1) Some(d.doubleValue) else None
}

Usage:

implicit val formatter = NumberFormat.getInstance(Locale.ENGLISH)

Console println parseDouble("184.33")
Console println parseDouble("hello, world")