Question

I have an interface written in C#, but when implementing it in F#, I noticed some oddities.

• The F# class has to be cast to the interface before C# can consume it
• After casting, WPF can’t read it’s properties (Bindings failed and SNOOP was unable to reflect on it)
• I can wrap the object in C# code and everything works fine.

the interface

public interface IInterpret {
  public string Name {get;}
  public IEnumberable<Project> Interpret(string text);
}

The F# Class

type Interpreter()=
  interface IInterpret with
    member x.Name = "FParsec Based"
    member x.Interpret(str) = Seq.empty

The code below fails to compile
The error is about Interpreter not implementing IInterpert

public ViewModel(){
  IInterpret i = new FSharpLib.Interperter(); 
}

This is my current workaround

public class MyProxy: IInterpret{
    private IInterpret _cover;

    public MyProxy()        {
        _cover = new FSharpLib.Interperter() as IInterpret;
    }
    public string Name { get { return _cover.Name; } }
    public IEnumerable<Project> Interpret(string text){
        return _cover.Interpret(text);
    }
}

Is there something I’m doing wrong with my F# class def, or is the proxy needed? I’m using the current VS2010 f#, not an out of band drop.

Answer 1

F# implements all interfaces explicitly. This means you must explicitly cast to the interface type.

I don’t know a ton about WPF binding to explicit interfaces, but see if these

http://leecampbell.blogspot.com/2008/09/generic-binding-in-wpf-through-explicit.html

http://social.msdn.microsoft.com/Forums/en-US/wpf/thread/92a2a3ba-74a6-4c79-9c75-f42d232a4dbf

help? (I just found them Bing-ing for “wpf binding explicit interfaces”.)

(Another alternative may be to do something like

type Interpreter()= 
    member x.Name = "FParsec Based" 
    member x.Interpret(str:string) = Seq.empty 
    interface IInterpret with 
        member x.Name = x.Name
        member x.Interpret(str) = x.Interpret(str)

where you “explicitly implement the interface implicitly”, if you pardon the confusing terminology.)