Mixin in C#
Tags: mixins, csharp, oop, developer
Published: 2023-08-04 17:32:51


In this post I will talk about Mixin concept and how to implement it in C# and I provide a code example to prove concept, So let's go ahead.

---

**Mixins** are a language concept that **allows a programmer to inject some code into a class.** Mixin programming is a style of software development, in which units of functionality are created in a class and then mixed in with other classes but which cannot itself be instantiated.


- Mixins are useful in object oriented languages which only support single inheritance Like C#, Java, Kotlin, etc.

- A mixin class **acts as the parent class**, containing the desired functionality.


- In order to implement a mixin in c# we will use a _combination of interfaces and extension methods_.

---

Let's dive into an example:

Consider the **Employee** Class that is a **Person** needs to use **work experience** functions


![interface to extend functionality from](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/c4da40svzisu2ob31d19.png)

Work experience extension methods:

![Work experience extension methods](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/mevve7o0saertssnxihi.png)

Employee Class: 

![Employee class](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/p7802vst4oftmbtvvk70.png)

So we can Simply get Employee Level:

![Client Using](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/wl33qsnjb48rw7u9gm6l.png)
**output**: `Name Refaat, Level = Junior`

---

**Does this mean that mixins can only have methods - what about fields?**
- No, they can have fields.
To do that we may apply a nested class contains needed fields and then associate the instance of this nested class with each object which implements the mixin interface.

will use **_ConditionalWeakTable_** collection to associate mixin classes with fields in the example to let garbage collector cleaning up these Fields.

[know more about ConditionalWeakTable](https://learn.microsoft.com/en-us/dotnet/api/system.runtime.compilerservices.conditionalweaktable-2?view=net-7.0)

**Final example**:
- Let's establish fields at _**WorkExperienceProvider**_ static class that contains extention methods

![Establish Fields](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/hjcbwn7pt8lsx7uem09y.png)

Put years of experience set & get extention methods:
![years of experience set & get extention methods](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/u9qt1mb3xl7i5v6v3gtk.png)

now we can update GetTechLevel method to not wait years of experience from client

![GetTechLevel method](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/sm5ztauae0yeu3ad4bnc.png)

Now we can get Employee Level:

![Client Using](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/2v8mka3d3psfkpkx0ifx.png)

**Output** `Name Esraa, Level = Junior`

**Code sample**

![Whole Code Example](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/nd8so2nfkunfifklykz9.png)

## Advantages

1. It provides a mechanism for multiple inheritance by allowing one class to use common functionality from multiple classes, but without the complex semantics of multiple inheritance.

2. Code reusability: Mixins are useful when a programmer wants to share functionality between different classes. Instead of repeating the same code over and over again, the common functionality can simply be grouped into a mixin and then included into each class that requires it.


Run code and trace it to more illustration, Have fun