Referential transparency

In Scala, referential transparency (RT) means that an expression or a function call may be replaced by its value, without changing the behavior of the application.

A value may be replaced by an expression or a function call without changing the behavior of the application.

We will explore these two points with some simple examples now.

Let's assume that we are using the y = x + 1 expression in our application:

scala> val x = 10 
x: Int = 10 
 
scala> val y = x + 1 
y: Int = 11 
 
scala> val y = 11 
y: Int = 11 

Here, when we replace an expression x+1 with its value 11, it does not change any behavior of the y in our application:

scala> val y = 11 
y: Int = 11 
 
scala> def addOne(a: Int) = a + 1 
addOne: (a: Int)Int 
 
scala> val y = addOne(x) 
y: Int = 11 

Here, the value of y is replaced by a function called addOne(). In this case...