Declaring and calling functions

A Scala function takes 0 to n parameters and returns a value. The type of each parameter must be declared. The type of the returned value is optional, as it is inferred by the Scala compiler when not specified. However, it is a good practice to always specify the return type, as it makes the code more readable:

scala> def presentation(name: String, age: Int): String = 
  "Hello, my name is " + name + ". I am " + age + " years old."
presentation: (name: String, age: Int)String

scala> presentation(name = "Bob", age = 25)
res1: String = Hello, my name is Bob. I am 25 years old.

scala> presentation(age = 25, name = "Bob")

res2: String = Hello, my name is Bob. I am 25 years old.

We can call a function by passing arguments in the right order, but we can also name the arguments and pass them in any order. It is a good practice to name the arguments when some of them have the same type, or when a function takes many arguments. It avoids passing the wrong argument and improves readability.