TWinControl.Controls Enumerator, Revisited

Fredrik Loftheim made an interesting observation to my previous article on TWinControl.Controls enumerator - namely that the enumerator factory doesn't have to be interface based. It can be replaced by a record. Source is almost the same as before, but we can skip the interface declaration. Generated code is simpler as the enumerator factory is simply allocated from the stack and automatically destroyed when it goes out of scope. No interface support and no reference counting is required. Simpler and faster, that's the way to go.

interface

type
  TControlEnumerator = record
  strict private
    ceClass : TClass;
    ceIndex : integer;
    ceParent: TWinControl;
  public
    constructor Create(parent: TWinControl; matchClass: TClass);
    function GetCurrent: TControl;
    function MoveNext: boolean;
    property Current: TControl read GetCurrent;
  end; { TControlEnumerator }

  TControlEnumeratorFactory = record
  strict private
    cefClass : TClass;
    cefParent: TWinControl;
  public
    constructor Create(parent: TWinControl; matchClass: TClass);
    function  GetEnumerator: TControlEnumerator;
  end; { TControlEnumeratorFactory }

function  EnumControls(parent: TWinControl; matchClass: TClass = nil): TControlEnumeratorFactory;

implementation

function EnumControls(parent: TWinControl; matchClass: TClass = nil): TControlEnumeratorFactory;
begin
  Result := TControlEnumeratorFactory.Create(parent, matchClass);
end; { EnumControls }

{ TControlEnumerator }

constructor TControlEnumerator.Create(parent: TWinControl; matchClass: TClass);
begin
  ceParent := parent;
  ceClass := matchClass;
  ceIndex := -1;
end; { TControlEnumerator.Create }

function TControlEnumerator.GetCurrent: TControl;
begin
  Result := ceParent.Controls[ceIndex];
end; { TControlEnumerator.GetCurrent }

function TControlEnumerator.MoveNext: boolean;
begin
  Result := false;
  while ceIndex < (ceParent.ControlCount - 1) do begin
    Inc(ceIndex);
    if (ceClass = nil) or (ceParent.Controls[ceIndex].InheritsFrom(ceClass)) then begin
      Result := true;
      break; //while
    end;
  end; //while
end; { TControlEnumerator.MoveNext }

{ TControlEnumeratorFactory }

constructor TControlEnumeratorFactory.Create(parent: TWinControl; matchClass: TClass);
begin
  cefParent := parent;
  cefClass := matchClass;
end; { TControlEnumeratorFactory.Create }

function TControlEnumeratorFactory.GetEnumerator: TControlEnumerator;
begin
  Result := TControlEnumerator.Create(cefParent, cefClass);
end; { TControlEnumeratorFactory.GetEnumerator }

The new version of the TWinControl.Controls enumerator plus some other stuff is available at http://gp.17slon.com/gp/files/gpvcl.zip.