Uniform Access Principle

The Scala language implements a programming concept known as the Uniform Access Principle, which was first put forth by Bertrand Meyer, the inventor of the Eiffel programming language.

This principle states that variables and parameterless functions should be accessed using the same syntax. Scala supports this principle by allowing parentheses to not be placed at call sites of parameterless functions. As a result, a parameterless function definition can be changed to a val, or vice versa, without affecting client code:

class Test1(val age: Int = 10)
class Test2(_age: Int) {
  def age: Int = _age

new Test1(10).age should be(res0)
new Test2(11).age should be(res1)