Question

When working with lists of items where the lists just serve as a temporary container – which list types would you recommend me to use?

I

• don’t want to destroy the list manually
• would like to use a built-in list type (no frameworks, libraries, …)
• want generics

Something which would make this possible without causing leaks:

function GetListWithItems: ISomeList;
begin
  Result := TSomeList.Create;
  // add items to list
end;

var
  Item: TSomeType;
begin
  for Item in GetListWithItems do
  begin
    // do something
  end;
end;

What options do I have? This is about Delphi 2009 but for the sake of knowledge please also mention if there is something new in this regard in 2010+.

Answer 1

The standard list classes, like TList, TObjectList, TInterfaceList, etc, do not implement automated lifecycles, so you have to free them manually when you are done using them. If you want a list class that is accessible via an interface, you have to implement that yourself, eg:

type
  IListIntf = interface
    ...
  end;

  TListImpl = class(TInterfacedObject, IListIntf)
  private
    FList: TList;
    ...
  public
    constructor Create; override;
    destructor Destroy; override;
    ...
  end;

constructor TListImpl.Create;
begin
  inherited;
  FList := TList.Create;
end;

destructor TListImpl.Destroy;
begin
  FList.Free;
  inherited;
end;

function GetListWithItems: IListIntf;
begin
  Result := TListImpl.Create;
  // add items to list
end;