Strange CLR error while handling Nullable types in Oxygene .net

Question

I'm writing a program in Oxygene .net There seems to be a problem with how I am handling nullable types

    namespace RULER;

interface

uses
  System,
  System.Drawing,
  System.Collections,
  System.Collections.Generic,
  System.Windows.Forms,
  System.ComponentModel;

type
  /// <summary>
  /// Summary description for Settings.
  /// </summary>
  Settings = public partial class(System.Windows.Forms.Form)
  private
      method Settings_Shown(sender: System.Object; e: System.EventArgs);
      method GetLowerBound : System.Nullable<Double>;
      method SetLowerBound(lowerbound:System.Nullable<Double>);
      method Settings_Load(sender: System.Object; e: System.EventArgs);
      method btnOK_Click(sender: System.Object; e: System.EventArgs);
  protected
      method Dispose(aDisposing: Boolean); override;
  public
      property LowerBound : System.Nullable<Double> read GetLowerBound write SetLowerBound;
    constructor;
  end;

implementation

{$REGION Construction and Disposition}
constructor Settings;
begin
  //
  // Required for Windows Form Designer support
  //
  InitializeComponent();

  //
  // TODO: Add any constructor code after InitializeComponent call
  //
end;

method Settings.Dispose(aDisposing: Boolean);
begin
  if aDisposing then begin
    if assigned(components) then
      components.Dispose();

    //
    // TODO: Add custom disposition code here
    //
  end;
  inherited Dispose(aDisposing);
end;
{$ENDREGION}

method Settings.Settings_Shown(sender: System.Object; e: System.EventArgs);
begin
    LowerBound := System.Nullable<Double>(Controller.configuration.LowerBound);
end;

method Settings.GetLowerBound : System.Nullable<Double>;
begin
    var bound : Double;
    if Double.TryParse(txtLowerBound.Text, out bound) then
    begin
        Result := bound;
    end else
    begin
        Result := System.Nullable<Double>(nil);
    end;
end;

method Settings.SetLowerBound(lowerbound:System.Nullable<Double>);
begin
    if lowerbound.HasValue then
    begin
        txtLowerBound.Text := lowerbound.Value.ToString;
    end else
    begin
        txtLowerBound.Text := '';
    end;
end;

method Settings.Settings_Load(sender: System.Object; e: System.EventArgs);
begin

end;

method Settings.btnOK_Click(sender: System.Object; e: System.EventArgs);
begin
    var LB : System.Nullable<Double> := Self.GetLowerBound;

    if LB.HasValue then
    begin
        Controller.configuration.LowerBound := LB.Value;
    end;
end;

end.

When I click the button firing the btnOK_Click event I get a strange error message

The runtime has encountered a fatal error. The address of the error was at 0x691886da, on thread 0x770. The error code is 0xc0000005. This error may be a bug in the CLR or in the unsafe or non-verifiable portions of user code. Common sources of this bug include user marshaling errors for COM-interop or PInvoke, which may corrupt the stack.

Answer 1

fwiw, i would suggest using Oxygene's built in "nullable" language feature, as it works m uch more transparent and intuitively than System.Nullable. e.g:

method Settings.GetLowerBound : nullable Double;
begin
    var bound : Double;
    if Double.TryParse(txtLowerBound.Text, out bound) then
    begin
        Result := bound;
    end else
    begin
        Result := nil;
    end;
end;

Regardless, getting "The runtime has encountered a fatal error." is indicative of a compiler error. I will log an issue on our side with your testcase.

Answer 2

This looks to be a compiler error. I've forwarded the information for RemObjects to file bug on this and fix it. In the mean time you might try a newer version (or maybe a beta).

Answer 3

I believe the solution is to replace

Result := System.Nullable<Double>(nil);

With

Result := new System.Nullable<Double>;