Interface + Extension (mixin) vs Base Class

Question

Is an interface + extension methods (mixin) preferable to an abstract class?

If your answer is \"it depends\", what does it depend upon?

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Answer 1

Interfaces tend to make code a little cleaner I feel it's a little easier to test. When you add Extensions your adding even more flexibility while keeping clean testable code.

For me abstract classes have always seemed clunky, using interfaces I can have an object factory that returns an object that is specific to what I'm trying to accomplish (separation of concerns).

Just making something up A have the interface called Math that has add, subtract, divide and multiply and then I have a class called IntMAth that implements Math that is optimized for integer math, and I have another class called FloatMath the implements Math that is optimized for Floating Math, and I have a generalMath that implements Math that handles everything else.

When I need to Add some floats I could call my factory MathFactory.getMath(typeof(float)) and it has some logic to know that if the type I'm passing in is a float then it returns the FloatMath class.

This way all of my classes are smaller and more maintainable, the code that calls the classes is smaller, etc.