Defining static classes in F#

Question

Is it possible to define a static class that contains overloadable members in F#? let module bindings cannot be overloaded, even though they are compiled into static static members in static classes.

type declerations can contain static members, but I don't know if the type itself can be made static.

My current solution is to define a type with a private constructor and just use that. I'm wondering if there is a way I can define a static type as I want.

Answer 1

As Robert Jeppeson pointed out, a "static class" in C# is just short-hand for making a class that cannot be instantiated or inherited from, and has only static members. Here's how you can accomplish exactly that in F#:

[<AbstractClass; Sealed>] type MyStaticClass private () =     static member SomeStaticMethod(a, b, c) =        (a + b + c)      static member SomeStaticMethod(a, b, c, d) =        (a + b + c + d) 

This might be a little bit of overkill, as both the AbstractClass and the private constructor will prevent you from creating an instance of the class, however, this is what C# static classes do - they are compiled to an abstract class with a private constructor. The Sealed attribute prevents you from inheriting from this class.

This technique won't cause a compiler error if you add instance methods the way it would in C#, but from a caller's point of view there is no difference.

Answer 2

This is explained in The F# Component Design Guidelines.

[<AbstractClass; Sealed>] type Demo =     static member World = "World"     static member Hello() = Demo.Hello(Demo.World)     static member Hello(name: string) = sprintf "Hello %s!" name  let s1 = Demo.Hello() let s2 = Demo.Hello("F#") 

It is still possible to define instance methods, but you can't instantiate the class when there is no constructor available.

edit Jan 2021 : See the comment from Abel, and the linked issue. Joel Mueller's answer seems to be the best advice so far, but things will perhaps change in the future.