Step by step

Folks,

For everybody thats use a lot Chained lists on your projects:

 Delphi | 
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001
uses SysUtils;
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type
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  PPointer = ^Pointer;
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  TChainedList = class
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  private
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    FFirst   : Pointer;
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    FLast    : Pointer;
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    FCurrent : Pointer;
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    FCount   : Integer;
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    function GetCurrent: PPointer;
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  public
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    constructor Create;
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    destructor Destroy; override;
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    function First : TChainedList;
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    function Last  : TChainedList;
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    function Prior : TChainedList;
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    function Next  : TChainedList;
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    function Add: TChainedList;
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    function Remove: TChainedList; overload;
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    function Remove(AChainedReleaser: Pointer): TChainedList; overload;
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    property Current: PPointer read GetCurrent;
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    property Count: Integer read FCount;
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  end;
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implementation
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type
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  PChainedItem = ^TChainedItem;
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  TChainedItem = record
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    Prior, Next: PChainedItem;
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    Data: Pointer;
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  end;
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{ TChainedList }
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constructor TChainedList.Create;
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begin
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  FCount := 0;
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  FFirst := nil;
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  FLast := nil;
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  FCurrent := nil;
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end;
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destructor TChainedList.Destroy;
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begin
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  First;
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  while Current <> nil do
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    Remove;
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  inherited;
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end;
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function TChainedList.GetCurrent: PPointer;
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begin
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  if FCurrent <> nil then
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    Result := @PChainedItem(FCurrent).Data
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  else
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    Result := nil;
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end;
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function TChainedList.First: TChainedList;
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begin
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  FCurrent := FFirst;
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  Result := Self;
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end;
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function TChainedList.Last: TChainedList;
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begin
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  FCurrent := FLast;
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  Result := Self;
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end;
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function TChainedList.Prior: TChainedList;
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begin
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  if FCurrent <> nil then
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    FCurrent := PChainedItem(FCurrent)^.Prior
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  else
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    FCurrent := nil;
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  Result := Self;
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end;
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function TChainedList.Next: TChainedList;
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begin
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  if FCurrent <> nil then
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    FCurrent := PChainedItem(FCurrent)^.Next
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  else
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    FCurrent := nil;
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  Result := Self;
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end;
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function TChainedList.Add: TChainedList;
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var
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  pNew: PChainedItem;
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begin
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  New(pNew);
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  pNew^.Prior := nil;
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  pNew^.Next := nil;
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  pNew^.Data := nil;
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  if FFirst = nil then
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  begin
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    FFirst := pNew;
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    FLast := pNew;
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  end else
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  begin
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    pNew^.Prior := PChainedItem(FLast);
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    PChainedItem(FLast)^.Next := pNew;
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    FLast := pNew;
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  end;
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  FCurrent := FLast;
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  Result := Self;
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  Inc(FCount);
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end;
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function TChainedList.Remove: TChainedList;
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var
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  pCur: PChainedItem;
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begin
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  pCur := FCurrent;
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  if pCur^.Data <> nil then
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    raise Exception.Create('Current item memory leak detected.');
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  if pCur^.Next <> nil then
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    pCur^.Next^.Prior := pCur^.Prior;
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  if pCur^.Prior <> nil then
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    pCur^.Prior^.Next := pCur^.Next;
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  if pCur = FFirst then
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  begin
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    FFirst := pCur^.Next;
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    FCurrent := FFirst;
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  end else if pCur = FLast then
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  begin
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    FLast := pCur^.Prior;
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    FCurrent := FLast;
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  end else
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    FCurrent := pCur^.Next;
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  Result := Self;
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  Dispose(pCur);
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  Dec(FCount);
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end;
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function TChainedList.Remove(AChainedReleaser: Pointer): TChainedList;
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type
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  TRelease = procedure(APointer: Pointer);
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var
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  PdrRelease: TRelease;
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begin
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  @PdrRelease := AChainedReleaser;
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  PdrRelease(PChainedItem(FCurrent)^.Data);
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  PChainedItem(FCurrent)^.Data := nil;
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  Result := Remove;
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end;

See how to use it here: Delphi: Chained List

Hugs!

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