Hi,

I have been having problems with the following code (the issue arises from the very end of it):

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type Chart =
class
 inherit Panel as base
 val Parent : Control ;
 val DataArea : Panel ;

 new (parent) as this = 
 {
  inherit Panel() ;
  Parent = parent ;
  DataArea = new Panel() ;
 }
 then
  this.SetStyle(ControlStyles.AllPaintingInWmPaint, true);
  this.SetStyle(ControlStyles.OptimizedDoubleBuffer, true);
  this.SetStyle(ControlStyles.ResizeRedraw, true);
  this.InitializeComponent ()
 
 member this.InitializeComponent () = 
  this.DataArea.BackColor <- Color.White ;
  this.DataArea.Dock <- DockStyle.Fill ;
  
  this.Controls.Add(this.DataArea) ; 
  
   
  let DrawCrosshair (control : #Control) (pen : Pen) x y =
   let g = control.CreateGraphics() in 
   g.Clear(control.BackColor) ;
   g.DrawLine(pen, x, 0, x, control.Height) ;
   g.DrawLine(pen, 0, y, control.Width, y) 
  in
  
  this.DataArea.MouseMove.Add(fun e -> DrawCrosshair this.DataArea (new Pen(Color.Black)) e.X e.Y) 
end

When I try to compile it as part of a larger chunk of code within the visual studio plugin, it works just fine. That is, I don't get any exception and the crosshair is drawn as expected.

However, when I try to invoke it form FSI, it raises an exception : System.TypeLoad Exception : Method 'Specialize' on type 'DrawCrossHair@3562' ... tried to implicitly override a method with weaker type parameter constraints ...

When I try to compile the whole projects, the compiler raises no error, but when the application is launched, I get the same exception.

(Note : I get the same type of exceptions from several locally-defined functions within another class.)

The various tries tend to show the error comes from this.DataArea.MouseMove.Add(fun e -> DrawCrosshair this.DataArea (new Pen(Color.Black)) e.X e.Y). Which is odd since a panel can be coerced to a control, as shows let f (c:#Control) = print_string c.Name in f (new Panel()).

Any idea as to how to solve this ?

Thanks a lot,

Julien.