Scala: match and parse an integer string?

Question

I'm looking for a way to matching a string that may contain an integer value. If so, parse it. I'd like to write code similar to the following:

  def getValue(s: String): Int = s match {
       case "inf" => Integer.MAX_VALUE 
       case Int(x) => x
       case _ => throw ...
  }

The goal is that if the string equals "inf", return Integer.MAX_VALUE. If the string is a parsable integer, return the integer value. Otherwise throw.

James Iry · Accepted Answer · 2009-07-02 20:29:11Z

41

Define an extractor

object Int {
  def unapply(s : String) : Option[Int] = try {
    Some(s.toInt)
  } catch {
    case _ : java.lang.NumberFormatException => None
  }
}

Your example method

def getValue(s: String): Int = s match {
  case "inf" => Integer.MAX_VALUE 
  case Int(x) => x
  case _ => error("not a number")
}

And using it

scala> getValue("4")
res5: Int = 4

scala> getValue("inf")
res6: Int = 2147483647

scala> getValue("helloworld")
java.lang.RuntimeException: not a number
at scala.Predef$.error(Predef.scala:76)
at .getValue(<console>:8)
at .<init>(<console>:7)
at .<clinit>(<console>)
at RequestResult$.<init>(<console>:4)
at RequestResult$.<clinit>(<console>)
at RequestResult$result(<console>)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Na...

answered Jul 2, 2009 at 20:29

James Iry

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4 Comments

Landon Kuhn Over a year ago

So you can just open up an object { } like that and add methods to an existing class? Cool (I think...).

Landon Kuhn Over a year ago

Never mind, I understand now that object Int{} is creating a new Int class in your namespace.

Daniel Spiewak Over a year ago

It actually might be more efficient to use regular expressions to match the contents of the string, rather than catching the exception.

Kevin Meredith Over a year ago

@DanielSpiewak, is that due to exceptions breaking Referential Transparency?

Xavier Guihot · Accepted Answer · 2022-04-16 07:06:32Z

11

This is better IMHO:

val IntRegEx = "(\\d+)".r
def getValue(s: String): Option[Int] =
  s match {
    case "inf"         => Some(Int.MaxValue)
    case IntRegEx(num) => Some(num.toInt)
    case _             => None
  }

getValue("inf")          // Some(2147483647)
getValue("123412")       // Some(123412)
getValue("not-a-number") // None

Of course, it doesn't throw any exceptions, but if you really want it, you may use:

getValue(someStr).getOrElse(error("NaN"))

edited Apr 16, 2022 at 7:06

Xavier Guihot

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answered Jul 4, 2013 at 19:41

rsenna

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2 Comments

NateH06 Over a year ago

If you pass "20100200300" as the value, you're going to get an exception. It'll pass your regex but that's (no moon) too big to be an Int and throw an exception.

rsenna Over a year ago

@NateH06 You're right, and the chosen answer does not have that flaw it seems. There should be a case catching those too-big number, or maybe we could use scala.math.BigInt instead.

cayhorstmann · Accepted Answer · 2011-06-19 10:55:36Z

8

You could use a guard:

def getValue(s: String): Int = s match {
  case "inf" => Integer.MAX_VALUE 
  case _ if s.matches("[+-]?\\d+")  => Integer.parseInt(s)
}

answered Jun 19, 2011 at 10:55

cayhorstmann

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Comments

Erik Kaplun · Accepted Answer · 2014-12-16 12:58:40Z

5

How about:

def readIntOpt(x: String) =
  if (x == "inf")
    Some(Integer.MAX_VALUE)
  else
    scala.util.Try(x.toInt).toOption

edited Dec 16, 2014 at 12:58

answered Oct 10, 2014 at 0:23

Erik Kaplun

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Comments

David Portabella · Accepted Answer · 2016-08-06 09:12:59Z

1

an improved version of James Iry's extractor:

object Int { 
  def unapply(s: String) = scala.util.Try(s.toInt).toOption 
}

answered Aug 6, 2016 at 9:12

David Portabella

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Comments

Xavier Guihot · Accepted Answer · 2019-07-01 20:01:24Z

1

Since Scala 2.13 introduced String::toIntOption:

"5".toIntOption   // Option[Int] = Some(5)
"abc".toIntOption // Option[Int] = None

we can cast the String as an Option[Int] after checking if it's equal to "inf":

if (str == "inf") Some(Int.MaxValue) else str.toIntOption
// "inf"   =>   Option[Int] = Some(2147483647)
// "347"   =>   Option[Int] = Some(347)
// "ac4"   =>   Option[Int] = None

edited Jul 1, 2019 at 20:01

answered Jan 18, 2019 at 15:34

Xavier Guihot

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Comments

agilefall · Accepted Answer · 2009-07-02 18:50:25Z

0

def getValue(s: String): Int = s match {
    case "inf" => Integer.MAX_VALUE 
    case _ => s.toInt
}


println(getValue("3"))
println(getValue("inf"))
try {
    println(getValue("x"))
}
catch {
    case e => println("got exception", e)
    // throws a java.lang.NumberFormatException which seems appropriate
}

answered Jul 2, 2009 at 18:50

agilefall

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1 Comment

Landon Kuhn Over a year ago

This is actually a good way to meet my immediate needs, however it's not the generic solution i was looking for. For instance, perhaps I would want to execute a block depending on what type the string was parsable to: def doSomething(s: String): Int = s match { case Int(x) => println("you got an int") case Float(x) => println("you got a float") case _ => throw ... }

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