Operator not applicable to this operand type when casting interfaces

Question

I've been working with a 3rd party service for the last couple days in Delphi XE2, and just about have it done. I'm running into a a problem that is absolutely stumping me that I think should have very obvious answers. I'm hoping another set of eyes can tell me what my problem is.

I have this interface:

IWorshipTeamEvent = Interface(IInterface)
  function GetId : integer;
  function GetName : string;
  function GetTeamId : integer;
  function GetStartDate : TDate;
  function GetEndDate : TDate;
  function GetStartTime : TTime;
  function GetEndTime : TTime;
  function GetSets : IWorshipTeamSetList;

  property Id : integer read GetId;
  property Name : string read GetName;
  property TeamId : integer read GetTeamId;
  property StartDate : TDate read GetStartDate;
  property EndDate : TDate read GetEndDate;
  property StartTime : TTime read GetStartTime;
  property EndTime : TTime read GetEndTime;
  property Sets : IWorshipTeamSetList read GetSets;
end;

Then in another class in the same unit, I'm trying to return a IWorshipTeamEvent in this function:

function TWorshipTeamEventList.GetEvent(index: Integer) : IWorshipTeamEvent;
begin
  //fEvents is a TInterfaceList that contains only IWorshipTeamEvents
  Result := fEvents[index] as IWorshipTeamEvent;
end;

At this point, I got the compiler error Operator not applicable to this operand type. I've tried a few things, like creating a temp variable with the type of IXmlResponseType and going

temp := fEvents[index] as IXmlResponseType;
Result := nil;

which compiled, so I tried creating temp with a type of IWorshipTeamEvent and going

temp := fEvents[index] as IWorshipTeamEvent;
Result := nil;

which did not compile.

Any suggestions are greatly appreciated

possible duplicate of Cast a TInterfacedObject to an interface — David Heffernan

nick nick · Accepted Answer · 2012-09-13T18:13:34

I read this answer on another question which pointed out that the GUID was missing. After Generating a GUID for my IWorshipTeamEvent interface, everything compiles and works as expected.

Operator not applicable to this operand type when casting interfaces

1 Answers