Question

This is a very elementary question about the F# class syntax. Here is a little code to illustrate my problem.

type AClass() as self =
    member this.Something = printfn "Hello"

Basically from what I have read the “as self” will create a name to the current instance which can be used in the entire class (like “this” in C# or Java). But “member this.Something” will do the same thing, only that the scope is limited to the method body. I guess I can see when you would use which syntax. The “as self” one can be used if you need it in the constructor or something and you can use the other one if you dont need it in the constructor.

But why do I have to use the “member this.Something” syntax even if I used the “as self” one? Why does it give me an error if I just write “member Something”? What have I missed?

Take care,
Kerr

Answer 1

The scope of as self is the whole class, while scope of this.Something is just an individual method. You don’t often need as self since using this.Something is adequate.

Regarding why you need this. in member declaration, I think it’s a natural choice since in F# classes you often have let bounds and static methods as well. Having self as default would cause confusion and misuse.

Here is an example using as self in MSDN, which is not common IMO:

type MyClass2(dataIn) as self =
   let data = dataIn
   do
       self.PrintMessage()
   member this.PrintMessage() =
       printf "Creating MyClass2 with Data %d" data