scala better syntax for map getOrElse

Question

is there a better way to write the code below?

val t = map.get(\'type).getOrElse(\"\"); 
if (t != \"\") \"prefix\" + t;

be interested in inline

Answer 1

It's also worth noting that, in certain cases, you can replace multiple common .getOrElse usages with one .withDefaultValue call.

val map = complexMapCalculation().withDefaultValue("")

val t = map('type)

I wouldn't say this is something that should be done every time, but it can be handy.

Answer 2

While reading the book Play for Scala, I picked up this code snippet that was defined in a controller, which might be a better syntax for getOrElse.

def show(ean: Long) = Action { implicit request =>

  Product.findByEan(ean).map { product =>
    Ok(views.html.products.details(product))
  }.getOrElse(NotFound)

}

In which, the Product.findByEan(ean: Long) was defined like

def findByEan(ean: Long) = products.find(_ean == ean)

Answer 3

Map has its own getOrElse method, so you can just write the following:

val t = map.getOrElse('type, "")

Which accomplishes the same thing as the definition of t in your first example.

---

To address your comment: If you know your map will never contain the empty string as a value, you can use the following to add the "prefix":

map.get('type).map("prefix" + _).getOrElse("")

Or, if you're using Scala 2.10:

map.get('type).fold("")("prefix" + _)

If your map can have "" values, this version will behave a little differently than yours, since it will add the prefix to those values. If you want exactly the same behavior as your version in a one-liner, you can write the following:

map.get('type).filter(_.nonEmpty).map("prefix" + _).getOrElse("")

This probably isn't necessary, though—it sounds like you don't expect to have empty strings in your map.

Answer 4

You could also use the Scalaz Zero typeclass so your code would look like below. The unary operator is defined on OptionW.

val t = ~map.get('type)                 // no prefix
val t = ~map.get('type).map("prefix"+_) // prefix

Here's an example session:

scala> import scalaz._; import Scalaz._
import scalaz._
import Scalaz._

scala> val map = Map('type -> "foo")
map: scala.collection.immutable.Map[Symbol,java.lang.String] = Map('type -> foo)

scala> ~map.get('type)
res3: java.lang.String = foo

scala> ~map.get('notype)
res4: java.lang.String = ""

scala> ~map.get('type).map("prefix"+_)
res5: java.lang.String = prefixfoo

scala> ~map.get('notype).map("prefix"+_)
res6: java.lang.String = ""