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Mutable static members?
f#compilerweb

I'm sure there is a pretty easily solution to this, but I've been going around and around with the compiler and the language specification for far too long, and can't figure out how the compiler wants me to express this. Basically, I want an object with a global counter. 

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type Foo = 
  class
    static member counter : int = 0
    val mycount : int
    new () as this { mycount = (let v = counter in (counter <- v+1; v))}
end

This naturally complains that counter isn't mutable, but I can't figure out how to make it so. I can't seem to add a mutable attribute to the static member declaration. I thought about adding a get/put augmentation, but it wasn't clear to me whether that really produces the correct semantics. val mutable counter doesn't do what I want because it makes it a per object member.

Also, is there a way that I can prevent this web page's JavaScript from making Firefox freak out quite so much?

.
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type Foo = 
  class
    static member counter : int = 0
    val mycount : int
    new () as this { mycount = (let v = counter in (counter <- v+1; v)) }
end

How about:

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let count =
   let n = ref 0 in
   fun () -> incr n; !n

Cheers,

Jon.

By on 10/23/2006 7:56 AM ()

As far as I know, it is currently not possible to declare static field in F#. My workaround for this is to create module with the value (which behaves just like static field) and to add static getter/setter to the class:

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module Foo_static = begin
  let counter = ref 1;
end;;

type Foo = class 
  new() = { }
  member this.counter
    with get() = !Foo_static.counter;
    and set(value) = Foo_static.counter := value; 
end;;
By on 10/13/2006 5:42 AM ()

F# pretty-printing in comments. Neat.

Yes, this is what I was going to do as a fall-back, but it felt better from an OO perspective to try to make it part of the class. I guess I'll worry about elegance later [:)]

It was at least my interpretation that static fields were possible, as the compiler didn't complain about my use of 

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 static member counter : int = 0

, unless this doesn't do what I thought it did. I suppose it could actually mean that counter is a static property with default get/set methods supplied.

Strangely enough, today Firefox isn't choking on the "composition" page's JavaScript. There really needs to be some exhaustive way to test implementations for "compliance".

By on 10/13/2006 6:28 AM ()

Hi,
I didn't realize it for the first time, but the 

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static member counter : int = 0

is compiled by the F# as a static method that returns 0, so unfortunately you'll have to use some "hack" for now. However I think that statics fields should be implemented in F# sooner or later.

By on 10/13/2006 12:09 PM ()

Hi guys,

Yep, Tomas' solution is the correct one for now. I agree we should support mutable static fields in classes.

Don

By on 10/14/2006 9:26 AM ()

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