Using Discriminated Unions In C#

I’ve reached the point where I needed discriminated unions but in C#, which doesn’t have support for it (yet). So, I’ve created a couple of classes (if you want a nuget they’re part of my CavemanTools library) that simulate a basic discriminated union with 2 or 3 options.

var fruits=new AnyOf<Apple,Orange>(new Apple());

fruits.When<Apple>(a=> {} );
fruits.When<Orange>(o=> {} );

//compile time type
var apple=fruits.As<Apple>();

//dynamic type
var apple=fruits.Value;

if (fruits.Is<Orange>()) {} 

Even if C# 7 will offer pattern matching, I still find useful to have a type that specifies and enforces only a couple of types; a dynamic field is just too generic.

And since option types won’t be available in C# 7 , I’ve also included an Optional struct for those moments when you really don’t want to deal with nulls .

private Optional<User> GetUser(){ }

var user=GetUser();

if (user.IsEmpty) {} 

var other=user.ValueOr(new User());

P.S: Inb4 “Why don’t you just use F# already?”. Because I know C# better, my F# knowledge is limited at this point and I need these features NOW. Besides, I only want a couple of features, not the whole language.

Written by Mike on 14 May 2016 | Topic: .net