Mixer

Mixin support for C#. When you can't inherit, include!

Mixer provides a smart [Include] attribute that copies the content of one type into another type. This enables you to 'inherit' from additional types beyond the single base class that C# allows.

For example, this code:

[Include<Pet>]
public partial class Dog : Mammal
{
    public void Bark() { ... }
}

[Mixin]
internal class Pet : IPet
{
    public string Name { get; set; }
}

compiles as if you had written:

public class Dog : Mammal, IPet
{
    public void Bark() { ... }

    public string Name { get; set; }
}

Some facts about this example:

Dog inherits the members of its base class, Mammal.
An instance of Dog can be cast to Mammal.
Through Mixer, Dog also includes the members, interfaces, and attributes of Pet.
An instance of Dog cannot be cast to Pet. C# allows only a single base class.
An instance of Dog can be cast to IPet.

Mixer is implemented as a Roslyn incremental generator for minimal impact to build times. For each inclusion, Mixer generates a partial type with the name of the target type and containing the members, base types, and attributes of the mixin.

Installation

Install this NuGet Package in your project.

Usage

To make a class, struct, or record become includable (i.e. a mixin), add the [Mixin] attribute to it.

using Mixer;

[Mixin]
internal class MyMixin { ... }

To include the mixin into some other class, struct, or record (i.e. a target type), make the target type partial and add the [Include] attribute to it. Mixer provides both generic and non-generic versions of this attribute.

using Mixer;

// C# 11 and later:

[Include<MyMixin>]
partial class MyTargetType { ... }

// Any verison of C#:

[Include(typeof(MyMixin))]
partial class MyTargetType { ... }

That's it!

Building from Source

If you have Visual Studio 2022, just open Mixer.sln and build as you would any other solution.

Or from PowerShell 7:

# The default: build and run tests
.\Make.ps1 [-Test] [-Configuration <String>]

# Just build; don't run tests
.\Make.ps1 -Build [-Configuration <String>]

# Build and run tests with coverage
.\Make.ps1 -Coverage [-Configuration <String>]

Advanced Topics

How do I see the generated code?

Add the following to the project file.

  <PropertyGroup>
    <EmitCompilerGeneratedFiles>true</EmitCompilerGeneratedFiles>
  </PropertyGroup>

Builds will drop the generated files into the following folder:

obj\{config}\{target}\generated\Mixer.Generator\Mixer.MixinGenerator\

To see the generated files in Visual Studio's solution explorer: