type
  TA=class(TInterfacedObject)

  end;

procedure TForm1.Button1Click(Sender: TObject);
var
  a:IInterface;
  [weak]aweak:IInterface;
begin
  a:=TA.Create;   //创建对象，复制给a，执行完成后引用计数器=1
  aweak:=a;       //由于aweak定义有[weak]属性，所以赋值给aweak后，引用计数器依旧为1，但aweak变量的地址被保存到一个weak关联列表中
  Memo1.Lines.Add(Format('Ptr:%d', [NativeInt(Pointer(aweak))]));
  a:=nil;         //由于引用计数器=1，执行此句后，计数器清0，对象被释放，同时与此对weak关联列表中所有变量也被赋值为nil，包括aweak变量.
  Memo1.Lines.Add(Format('Ptr:%d', [NativeInt(Pointer(aweak))]));
end;

Ptr:16360080
Ptr:0

type 
ISimpleInterface = interface 
  procedure DoSomething; 
  procedure AddObjectRef (simple: ISimpleInterface); 
end; 

TObjectOne = class (TInterfacedObject, ISimpleInterface) 
private 
  anotherObj: ISimpleInterface; 
public 
  procedure DoSomething; 
  procedure AddObjectRef (simple: ISimpleInterface); 
end;

.....................

procedure TObjectOne.AddObjectRef (simple: ISimpleInterface); 
begin
  anotherObj:=simple;
end;

.....................

var 
  one, two: ISimpleInterface; 
begin 
  one := TObjectOne.Create; 
  two := TObjectOne.Create; 
  one.AddObjectRef (two); 
  two.AddObjectRef (one);

private 
  [weak] anotherObj: ISimpleInterface;

type
  TA=class(TInterfacedObject)

  end;
procedure TForm1.Button2Click(Sender: TObject);
var
  a:IInterface;
  [unsafe]aunsafe:IInterface;
begin
  a:=TA.Create;
  aunsafe:=a;
  Memo1.Lines.Add(Format('Ptr:%d', [NativeInt(Pointer(aunsafe))]));
  a:=nil;
  Memo1.Lines.Add(Format('Ptr:%d', [NativeInt(Pointer(aunsafe))]));
end;

Ptr:42640064
Ptr:42640064

procedure TForm1.Button2Click(Sender: TObject); 
var 
  [unsafe] one: ISomeInterface;
begin 
  one := TSomeObject.Create; 
  one.DoSomething;
end;