LearningScala

Evaluantion

• Call by value "In call by value, the argument expression is evaluated, and the resulting value is bound to the corresponding variable in the function " Wikipedia
• Call by name "Call by name is an evaluation strategy where the arguments to a function are not evaluated before the function is called" Wikipedia

Functions

Higher order functions

"Higher order functions take other functions as parameters or return a function as a result." Higher-order Functions

Nested functions

def factorial(x: Int): Int = {
   def fact(x: Int, accumulator: Int): Int = {
     if (x <= 1) accumulator
     else fact(x - 1, x * accumulator)
   }  
   fact(x, 1)
}

println("Factorial of 2: " + factorial(2))
println("Factorial of 3: " + factorial(3))

Anonymous functions

"[...] anonymous function is also known as a function literal. A function which does not contain a name is known as an anonymous function. An anonymous function provides a lightweight function definition. It is useful when we want to create an inline function." Anonymous Functions in Scala

(z:Int, y:Int)=> z*y
// Or
(_:Int)*(_Int)

Infix Notation

Scala has a special punctuation-free syntax for invoking methods of arity-1 (one argument). This should generally be avoided, but with the following exceptions for operators and higher-order functions. In these cases it should only be used for purely-functional methods (methods with no side-effects). Method Invocations

Companion Objects

A companion object in Scala is an object that’s declared in the same file as a class, and has the same name as the class. For instance, when the following code is saved in a file named Pizza.scala, the Pizza object is considered to be a companion object to the Pizza class:

class Pizza {
}

object Pizza {
}

(Predef Object)[https://www.scala-lang.org/api/2.13.6/scala/Predef$.html#require(requirement:Boolean):Unit]

The require method is used to check preconditions such as whether a value is equal to another value.