TCollection

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unit uhair;

{$mode objfpc}{$H+}

interface

uses
  Classes, SysUtils, Dialogs;

type

  { THairItem }

  THairItem = class(TCollectionItem)
  private
    FLength: integer;
  public
    constructor Create(ACollection: TCollection); override;
  published
    property Length: integer read FLength write FLength;
  end;

  { THairList }

  THairList = class(TCollection)
  private
    function GetItems(Index: integer): THairItem;
    procedure SetItems(Index: integer; AValue: THairItem);
  public
    constructor Create;
  public
    function Add: THairItem;
    function AddEx(length: integer): THairItem;
    property Items[Index: integer]: THairItem read GetItems write SetItems; default;
  end;

var
  hairs: THairList;

implementation

{ THairItem }

constructor THairItem.Create(ACollection: TCollection);
begin
  if Assigned(ACollection) and (ACollection is THairList) then
    inherited Create(ACollection);
end;

{ THairList }

function THairList.GetItems(Index: integer): THairItem;
begin
  Result := THairItem(inherited Items[Index]);
end;

procedure THairList.SetItems(Index: integer; AValue: THairItem);
begin
  Items[Index].Assign(AValue);
end;

constructor THairList.Create;
begin
  inherited Create(THairItem);
end;

function THairList.Add: THairItem;
begin
  Result := inherited Add as THairItem;
end;

function THairList.AddEx(length: integer): THairItem;
begin
  Result := inherited Add as THairItem;
  Result.Length := length;
end;

initialization
  hairs := THairList.Create;
  hairs.AddEx(10);
  hairs.Add.Length := 100;
  hairs.Delete(0);

  ShowMessage(IntToStr(hairs.Count));

finalization
  hairs.Free;

end.