Hax
Table of Contents
Scala LyfHax.
1. Unapplying a String Interpolator
Since 2.13 you can use unapply with string interpolators:
"0 13 * * * echo 'Every day at 1pm'" match { case s"$min $hour $dayOfMonth $month $dayOfWeek $cmd" => Some(cmd) case _ => None } // Option[String] = Some("echo 'Every day at 1pm'")
2. null to Option
We can easily turn possible null values into an Option via apply:
val myString: String = null Option(myString) // Option[String] = None
Note without the type hint here the Option will have type Option[Null].
3. Apply on Different Data Structures
3.1. Lists
We can use the apply method on List objects to obtain the value at an index, but beware this is not safe, lift is usually a better option.
val myList = List(1, 2, 3) myList(1) // 2 myList(3) // java.lang.IndexOutOfBoundsException: 3 // scala.collection.LinearSeqOps.apply(LinearSeq.scala:117) // scala.collection.LinearSeqOps.apply$(LinearSeq.scala:114) // scala.collection.immutable.List.apply(List.scala:79)
apply on Maps, Strings, Arrays, Ranges, Vectors and Seqs behaves similarly.
3.2. Sets
apply on Sets can be used to test membership:
val bellsLt1k = Set(1, 2, 5, 15, 52, 203, 877) bellsLt1k(203) // true bellsLt1k(10) // false
4. For Comprehension One-liner
val rollOfTwoDie = (for (x <- (1 to 6); y <- (1 to 6)) yield x + y).sorted // Vector(2, 3, 3, 4, 4, 4, 5, 5, 5, 5, 6, 6, 6, 6, 6, 7, 7, 7, 7, 7, 7, 8, 8, 8, 8, 8, 9, 9, 9, 9, 10, 10, 10, 11, 11, 12)
5. Tuple to Case Class
We can use the .tupled method of FunctionN to nicely obtain a case class instance from a tuple:
case class Book(title: String, author: String) val bookData = ("Old Man's War", "John Scalzi") // Pre Scala 2.11.8 val book1 = (Book.apply _).tupled(bookData) // The companion object of case class extends FunctionN so we can do this is 2.11.8+ val book2 = Book.tupled(bookData)
6. Quicksort
Obligatory quicksort implementation:
import scala.math.Ordering.Implicits._ def quicksort[A: Ordering](l: List[A]): List[A] = { l match { case Nil => Nil case head :: tail => val (before, after) = tail.partition(_ <= head) (before :+ head) ::: after } }
7. Capturing Standard Output
You can easily capture standard output using Console.withOut. This saves you from having to reset the output stream when you're done if you were to use System.setOut.
val baos = new java.io.ByteArrayOutputStream() // Note println is an alias for Console.println Console.withOut(baos)(println("hello")) println(baos) // "hello"