IInfo needs a property that indicates if the object holds a value

[Anders Melander]

In methods and functions that take optional parameters I have previously tested IInfo.Value against Unassigned to determine if a parameter holds a value:

procedure TDataModuleMyStuff.dwsUnitBlahFooMethodsGetValueEval(Info: TProgramInfo; ExtObject: TObject);
begin
    if (Info.Params[0].Value = Unassigned) then
      // ...do something when parameter isn't supplied...
end;

After some recent changes this test now fails with a variant conversion error (can't compare a variant of type varEmpty with one of type varUnknown). Fair enough.

So instead I'm now doing this:

procedure TDataModuleMyStuff.dwsUnitBlahFooMethodsGetValueEval(Info: TProgramInfo; ExtObject: TObject);
begin
    if (VarIsEmpty(Info.Params[0].Value)) then
      // ...do something when parameter isn't supplied...
end;

However IMO both solutions are wrong as they rely on implementation details of IInfo's use of variants.

It would be better if IInfo provided a boolean property that indicated if it held a value or not. Something like IInfo.Assigned, IInfo.Empty or IInfo.IsNull.

[Anders Melander]

Expanding on the above, for some parameter types it is currently possible to test the value IInfo.ScriptObj against nil:

if (Info.Params[0].ScriptObj <> nil) then
  ...

However this is not possible for the function parameter type TInfoFunc.

Given the following script declaration:

type TCallback = procedure;
procedure Test(Callback: TCallback = nil);

the Delphi-side test for a specified parameter will fail. Since TInfoFunc.FScriptObj is nil the call to TInfoData.GetScriptObj will end up calling TInfo.GetScriptObj which raises an exception: Operation "IInfo.Obj" not possible on a symbol of type blah blah... (the error message probably needs to be brought up to date, btw).

[Eric Grange]

Fixed Issue #36, added IInfo.ValueIsEmpty + test

→ <<cset 491616730681>>