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  • Variance Examples

    February 28, 2014

    Variance Examples


    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]) {}