Scala.md

Scala

• Worksheet
• Basic methods
• infix operator notation
• Functions
• High order functions
• Custom types

Worksheet

A worksheet is a Scala file that is evaluated on save, and the result of each expression is shown in a column to the right of your program.

Basic methods

3.*(2)
(1: Int).toDouble
1.2.toInt

Scala has two types of variables:

• val (value) creates an immutable variable (like final in Java)
• var (variable) creates a mutable variable

blocks

val v3 = {
  val v1 = 1
  val v2 = v1 + 1
  v2 + 1
}

In Scala, the Unit type is a subtype of the AnyVal type. It denotes a method that doesn't return any meaningful result

var v4 = {}
v4 == ()

def ??? : Nothing = throw new NotImplementedError

If we don't want implement method we can use ???

def f(a: String): String = ???  

Infix operator notation

If a method takes a single argument, you can call it without the period after the instance and without parentheses around the argument.

For example, if I have a Matrix class and a + method to add matrices, element by element, I can write matrix1.+(matrix2) or use the less cluttered and more intuitive syntax, matrix1 + matrix2.

However, there was no restriction on what methods applied in Scala 2, so if I also had a plus method, then matrix1 plus matrix2 was allowed.

Functions

Functions are expressions that have parameters, and take arguments. You can define an anonymous function.

On the left of => is a list of parameters. On the right is an expression involving the parameters.

var sqr: Int => Int = (x: Int) => x * x

var sqr2: Int => Int = x => x * x
var sum: (Int, Int) => Int = _ + _

var sqr3 = new Function[Int, Int] {
  override def apply(v1: Int): Int = v1 * v1
}

var factorial: Int => Int =
  n => if (n == 0) 1 else n * factorial(n - 1)

Custom types