#754 – Downcast to a Reference to a Derived Class

If you have a variable that is a reference to a parent class, but it actually refers to an instance of a derived class, you can use a downcast operation to assign the reference to a variable whose type matches the derived class.

For example, assume that you have a Dog class and a Terrier class, which inherits from Dog.  You might have a reference to a Dog that actually refers to an instance of a Terrier.  To get at methods that are unique to Terrier, you’d downcast the Dog reference to a Terrier reference.

This type of conversion is known as a reference conversion.

            // Dog reference that points to a Terrier
            Dog d = new Terrier("Jack", Terrier.GrowlFactor.Severe);

            // Can't invoke Terrier methods via Dog reference
            //d.DoTerrierDance();   // ERROR

            // Downcast to Terrier.  Need explicit conversion
            Terrier t = (Terrier)d;

            // Can now treat like Terrier
            t.DoTerrierDance();
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About Sean
Software developer in the Twin Cities area, passionate about .NET technologies. Equally passionate about my own personal projects related to family history and preservation of family stories and photos.

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