Question

I come from a C++ background where I can use template mixins to write code that refers to FinalClass which is a template parameter that is passed in. This allows reusable functions to be ‘mixed-in’ to any derived class, by simply inheriting from ReusableMixin with a template paramter of MyFinalClass. This all gets inlined into the class so it’s as though I just wrote a big class that did everything — ie very fast! Since mixins can chain, I can mix-in all sorts of behaviour (and state) into one object.

If anyone wants clarification on the technique, please ask. My question is, how can I get reuse like that in C#? Note: C# generics don’t allow inheriting from a generic parameter.

Answer 1

In C#, the closest you get to C++ style mixins is adding the mixins as fields of a class and add a bunch of forwarding methods to the class:

public class MyClass {     private readonly Mixin1 mixin1 = new Mixin1();     private readonly Mixin2 mixin2 = new Mixin2();      public int Property1     {         get { return this.mixin1.Property1; }         set { this.mixin1.Property1 = value; }     }      public void Do1()     {         this.mixin2.Do2();     } } 

This is usually enough, if you only want to import functionality & state of the mixins. A mixin can of course be implemented as you like, complete with (private) fields, properties, methods, etc.

If your class also needs to express ‘is-a’ relationships with the mixins then you need to do the following:

interface IMixin1 {     int Property1 { get; set; } }  interface IMixin2 {     void Do2(); }  class MyClass : IMixin1, IMixin2 {     // implementation same as before } 

(This is also the standard way how multiple inheritance is emulated in C#.)

Of course, the mixin interfaces as well as the mixin classes can be generics, e.g. with a most-derived class parameter or whatever.