Uniform Access Principle in Scala

The Uniform Access Principle basically states that the notation used to access the object's member should be the same independent of whether the member is a field or a method. Thus the developer can remain ignorant of the actual implementation.

The Scala compiler automatically adds the getter/setter methods for constructor arguments depending on the type qualifier.  

class Person(var name: String)

For the above class, the Scala compiler generates the following Java class which can be obtained after disassembling the Person.scala. You can clearly see that getter & setter methods have been added automatically 

$ javap -p Person.class 

Compiled from "Person.scala"

public class Person {

  private java.lang.String name;

  public java.lang.String name();

  public void name_$eq(java.lang.String);

  public Person(java.lang.String);

}

Note the special syntax for the setter which is suffixed with "_$eq". This allows the setter to be invoked when an assignment style syntax is employed:

• If type = var, both getter/setter methods are added

• if type = val, only getter is added

• if no type is specified, neither getter/setter methods are added

val person1 = new Person("Alice")

println(person1.name) // The getter is invoked here implicitly here

person1.name = "Bob"  // The setter is invoked implicitly here

As is evident, the notation employed to access name field does NOT indicate whether the field is being accessed directly or the getter/setter method is being invoked. This is the Uniform Access Principle in action.