Partial functions

Partial functions do not suffice for every input given, which means these are defined to serve a purpose for a specific set of input parameters. To understand more, let's first define a partial function:

scala> val oneToFirst: PartialFunction[Int, String] = { 
     | case 1 => "First" 
     | } 
oneToFirst: PartialFunction[Int, String] = <function1> 
 
scala> println(oneToFirst(1)) 
First 

In the preceding code, we defined a partial function named oneToFirst. We also specified type parameters for our partial function; in our case we passed Int, String. The PartialFunction function is a trait in Scala, defined as:

trait PartialFunction[-A, +B] extends (A) => B 

The trait as shown expects two parameters A and B, that become the input and output types of our partial function. Our oneToFirst partial function simply expects 1 and returns a string representation for 1 as first. That's why when we try to call the function by passing 1, it works fine; but if we try...