How do you set a variable defined as the base class type to a derived type instance in Scala? -

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In Java, I can declare a variable as a base class type, and in a derivative type of example I can set: 

  Public class MyClass {base foo; Public Null Method () {foo = new derived ()}} I   class  class class received by MyClass {var foo: Base = _ // Carefully, this is empty unless it starts the DRIT method () = {foo = becomes new}}

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