// *** before: ***
// assigning a record copied its bytes. If the record owned a pointer or
// an object, both copies now pointed at the same thing, and the second
// destructor freed it twice
type
  TBuffer = record
    Data: Pointer;
    Size: Integer;
  end;

var
  A, B: TBuffer;
begin
  B := A;               // one buffer, two owners
end;

// *** in version 10.4: ***
type
  TBuffer = record
  public
    Data: Pointer;
    Size: Integer;
    class operator Initialize(out Dest: TBuffer);
    class operator Finalize(var Dest: TBuffer);
    class operator Assign(var Dest: TBuffer; const [ref] Src: TBuffer);
  end;

class operator TBuffer.Assign(var Dest: TBuffer; const [ref] Src: TBuffer);
begin
  FreeMem(Dest.Data);
  Dest.Size := Src.Size;
  GetMem(Dest.Data, Dest.Size);
  Move(Src.Data^, Dest.Data^, Dest.Size);   // a copy of its own
end;

var
  A, B: TBuffer;
begin
  B := A;               // the operator runs, and each side owns its own
end;