Talk:Declarations and Statements (Delphi)

Better example of code demonstrating iterating over an enumerable container in Delphi

The example on the help page is misleading. The data is stored in the enumerator class instead of the container! The example below has data into the container (Values in TMyContainer) and has a class to enumerate which only enumerate data in the container.

type
  TMyIntArray   = array of Integer;
  TMyContainerEnumerator = class;

  TMyContainer  = class
  public
    Values: TMyIntArray;
    function GetEnumerator: TMyContainerEnumerator;
  end;

  TMyContainerEnumerator = class
    Container : TMyContainer;
    Index     : Integer;
  public
    constructor Create(AContainer : TMyContainer);
    function GetCurrent: Integer;
    function MoveNext:   Boolean;
    property Current:    Integer read GetCurrent;
  end;

constructor TMyContainerEnumerator.Create(AContainer : TMyContainer);
begin
  inherited Create;
  Container := AContainer;
  Index     := - 1;
end;

function TMyContainerEnumerator.MoveNext: Boolean;
begin
  Result := Index < High(Container.Values);
  if Result then
    Inc(Index);
end;

function TMyContainerEnumerator.GetCurrent: Integer;
begin
  Result := Container.Values[Index];
end;

function TMyContainer.GetEnumerator: TMyContainerEnumerator;
begin
  Result := TMyContainerEnumerator.Create(Self);
end;

var
  MyContainer : TMyContainer;
  I           : Integer;
  Counter     : Integer;
begin
  MyContainer        := TMyContainer.Create;
  MyContainer.Values := TMyIntArray.Create(100, 200, 300);

  Counter := 0;
  for I in MyContainer do
    Inc(Counter, I);

  Writeln('Counter = ', Counter, ' (should be 600)');
  ReadLn;
end.

Response

Thank you, Francois, for your code example. We are evaluating the example and will add it to the docwiki if the team agrees.

Many thanks for your input -

KrisHouser (talk) 16:48, 3 January 2013 (PST)

RS-34754

Example of a For Loop through a set based on an enumerated type

procedure TForm1.Button1Click(Sender: TObject);
type
 Tcol = (cred, cgreen, cblue, cyellow);
 Tcols = set of Tcol;
var
 Colors: Tcols;
 col: Tcol;
 S: string;
begin
  Colors := [cyellow, cblue, cgreen];
  S := '';
  for Col in Colors do  // loop through colors in the set
  begin
   case Col of
     cred: S := S + ' red';
     cgreen: S := S + ' green';
     cblue: S := S + ' blue';
     cyellow: S := S + ' yellow';
   end;
  end;
  ShowMessage(S);  // uses Dialogs
end;