Variance Examples

February 28, 2014

Variance Examples

Hi,

today I would to introduce scala some. variance examples. Those magic +A -A what is it ?

I will show by the example, first declaring classes:

class Boss
class Worker extends Boss
class Student extends Worker

class TestClass[A]
class TestCovariantClass[+A]
class TestContravariantClass[-A]

Now decalring methods which takes as a param one of our Test classes:

// here will go Worker class only

def testMethod(x: TestClass[Worker]) {}

// Worker and Student

def testMethod2(x: TestCovariantClass[Worker]) {}

// Worker and Boss

def testMethod3(x: TestContravariantClass[Worker]) {}