Question

This must be a Delphi bug…

I have a unit which is the basis of my persistance framework. In that unit I have a base class for all my domain objects, a list class and a generic list class.

Just recently I noticed that when I step into the unit when debugging, execution will jump to a point a little further down in the file than it should… Maybe four or five lines. Re-ordering the file makes no difference. The code would also generate access violations, but only when I debugged it.

I cast about trying to find the reason for this… Several things came to mind, like some code injection screwing with the debugger (eg this logitec webcam driver bug), or the debug info being out of sync with my unit source (eg the dcu was being pulled from some old source).

In the end I fired up a VM with a clean Windows + Delphi install, grabbed only what I needed to test the unit, and I created a small DUnit project to test it. Same problem.

Then I started removing things from the unit one at a time till it worked. The only thing that made any difference was when I removed the generic list class.

Has anyone else seen this problem? Does anyone know how to get around it?

Thanks in advance,

N@

Update: Adding the generic back into the unit makes the problem come back, so it’s not a problem of stale DCUs.

Answer 1

In the end, the only solution that I could find that worked was to move the generic list out of the Unit.

Update 2011-08-03 To better flesh out my solution:

I had my generic list base class defined in my Domain unit with my base TDomainObject class and a non-generic version.

To fix the problem, I moved the generic into a second Domain.Generics unit which resolved the problem for me.

So:

unit Domain;

interface 

type
  TDomainObject = class
    //blah de blah
  end;

  TDomainObjectList = class (TDomainObject)
    //more stuff
  end;

  TDomainListEnumerator = class
    //etc
  end;

And:

unit Domain.Generics;

interface

type

  TDomainObjectList<T: TDomainObject> = class (TDomainObjectList)
    //stuff
  public
    property Items[AIndex: integer]: T read GetItem write SetItem;

    type
      TEnumerator = class (TDomainListEnumerator)
      public
        function GetCurrent: T;
        property Current: T read GetCurrent;
      end;

  public
    function GetEnumerator: TEnumerator;

  end;