Simple Interface demo.

Interfaces.dpr

program Interfaces;

{$APPTYPE CONSOLE}

{$R *.res}


uses
  LeakCheck,
  System.Classes, System.SysUtils;

type
  IFoo = interface(IInterface)
    ['{EB3BBAA4-6176-48E1-9419-2D6B2B5C6B67}']
    procedure Something;
  end;

  TFoo = class(TInterfacedObject, IFoo)
  public
    procedure Something;
  end;

procedure DoSomething;
begin
  //Create an instance of TFoo
  var LFoo: IFoo := TFoo.Create;
  //Do something with that instance
  LFoo.Something;
  //No need to cleanup. LFoo goes out of scope, which will trigger TFoo's destructor.
end;

{ TFoo }

procedure TFoo.Something;
begin
  Writeln('Something');
end;

begin
  ReportMemoryLeaksOnShutdown := true;
  try
    //Do esomething that creates a couple of TFoo instances
    DoSomething;
    DoSomething;
    // All instances of TFoo are gone here, as they are no longer in use here.
  except
    on E: Exception do
      Writeln(E.ClassName, ': ', E.Message);
  end;
  Readln;

end.

Two notes:

1. When using inline variables, as I do in the example, make sure that you explicitly type them as Interface. By default, the automatically inferred type will be the corresponding class type.
2. Under certain conditions, the built-in memory manager (which is a FastMM fork), does not reliably detect memory leaks. LeakCheck is cross-platform and seems to be more reliable in corner cases. This sample, in D11.0.2, would not detect a leak with LFoo typed as TFoo, if using the built-in MM.