I'm not sure what is the best way to define Unit for usage from C#. It might differ from how this is done in F# (because in F#, the compiler hides the usage in a way).

However, you can actually find the implementation of F# unit in the core library:

• The public interface is defined in prim-types.fsi
• The implementation is provided in prim-types.fs

Here are the key points about the F# unit implementation

• It implements GetHashCode and Equals in the same way to the Rx version
• It is IComparable and all values of the unit type are equal
• Most importantly, it has a private constructor and so you cannot create a new unit value. It also has no default instance (unlike the Rx unit) and so in F#, all unit values are actually represented as null. However, the language/compiler generally hide this fact.

So, it sounds like the only difference in F# is that it uses the null value. If you want to use unit explicitly, this might not be the best choice. However, if you have Unit.Default then you are ultimately defining a type with two possible values, because it can be either Unit.Default or null (and so it is not really a unit!)

System.ValueTuple (without generic argument) is very much unit in C#. The source code is open.

I have used this Unit type as a reference: https://github.com/louthy/language-ext/blob/main/LanguageExt.Core/DataTypes/Unit/Unit.cs

Coming from a functional extension library.