A simple Generic List: TList<T>

Delphi 2009 has support for generics, and has 'built in' generic types like TList, TArrays etc. If you want to use them you must add Generics.Collections to your uses clause.

Generic List: TList
Suppose we want a list with persons representing the TPerson class:

// Our class TPerson
type
  TPerson = class
   FFirstName : string;
   FLastName : string;
  private
    function GetFullName: string;
  published
  public
    constructor Create(ALastName : String; 
                            AFirstName : string);
    property FirstName : string read FFirstName 
                             write FFirstName;
    property LastName : string read FLastName 
                             write FLastName;
    property FullName : string read GetFullName;
  end;

//Define the generic list
PersonsList : TList<TPerson>;

//Method to fill the list
procedure TForm4.btnPopulateClick(Sender: TObject);
begin
  //Filll the personslist
  PersonsList.Add(TPerson.Create('Delphi','James'));
  PersonsList.Add(TPerson.Create('Generic','Mister'));
  PersonsList.Add(TPerson.Create('Anon', 'Method'));
  //etc.
end;

//Traveling this list to fill a TListBox
procedure TForm4.FillListBox;
var
  p : TPerson;
begin
  ListBox1.Items.Clear;
  for p in PersonsList do begin
    ListBox1.Items.Add(p.FullName);
  end;
end;

As you can see, no rocking science needed to implement a generic list!

Sorting a generic TList
The next step is to implement a sorting method to sort the list on, for example, the Lastname property.

A TList has a Sort property which has an IComparer interface that can be implemented like this using an anonymous method:

(You will have to add generics.default to your uses clause)

procedure TForm4.btnSortClick(Sender: TObject);
begin
  PersonsList.Sort(TComparer<TPerson>.Construct(
      function(const Item1,Item2:TPerson): Integer
      begin
         Result := 
          CompareText(Item1.LastName, Item2.LastName);
      end));
end;

Generics is a great new feature of Delphi 2009. Just as in C# you will use them all the time. In this context, the use of anonymous methods is great.

Besides TList Delphi has more standard generics typs including TArray, TEnumarable and more, so there is always more to explore!

Update 25-09-2008 10:58
As animal commented you must of course create the list first, which I did not include in the code snippets.

PersonsList:= TList.Create;

And you will have to free it also at sometime. (Don't forget to free the TPerson objects as well!)

for p in PersonsList do begin
p.free;
end;
PersonsList.Free;