1:
2:
3:
4:
5:
6:
7:
8:
9:
10:
11:
12:
13:
14:
15:
16:
17:
18:
19:
20:
21:
22:
23:
24:
25:
26:
27:
28:
29:
30:
31:
32:
33:
34:
35:
36:
37:
38:
39:
40:
41:
42:
43:
44:
45:
46:
47:
48:
49:
50:
51:
52:

type
  TFoo = record
    Value: TBytes;
    class operator Add(const Value1, Value2: TFoo): TFoo;
    class operator implicit(const AValue: AnsiString): TFoo;
    class operator implicit(const AValue: TFoo): TBytes;
    class operator implicit(const AValue: TFoo): AnsiString;
    procedure LoadFromStream(const AStream: TStream; const ASize: Integer = -1);
    procedure SaveToStream(const AStream: TStream);
  end;

[...]

class operator TFoo.Add(const Value1, Value2: TFoo): TFoo;
begin
  SetLength(Result.Value, Length(Value1.Value) + Length(Value2.Value));
  CopyMemory(@Result.Value[0], @Value1.Value[0], Length(Value1.Value));
  CopyMemory(@Result.Value[Length(Value1.Value)], @Value2.Value[0], Length(Value2.Value));
end;

class operator TFoo.implicit(const AValue: AnsiString): TFoo;
begin
  SetLength(Result.Value, Length(AValue));
  CopyMemory(@Result.Value[0], PByte(AValue), Length(AValue));
end;

class operator TFoo.implicit(const AValue: TFoo): TBytes;
begin
  Result := AValue.Value;
end;

class operator TFoo.implicit(const AValue: TFoo): AnsiString;
begin
  SetLength(Result, Length(AValue.Value));
  CopyMemory(PByte(Result), @AValue.Value[0], Length(AValue.Value));
end;

procedure TFoo.LoadFromStream(const AStream: TStream; const ASize: Integer = -1);
var
  BytesAvail: Integer;
begin
  BytesAvail := AStream.Size - AStream.Position;
  if (ASize >= 0) and (ASize <= BytesAvail) then
    BytesAvail := ASize;
  SetLength(Value, BytesAvail);
  AStream.Read(Value, BytesAvail);
end;

procedure TFoo.SaveToStream(const AStream: TStream);
begin
  AStream.Write(Value, Length(Value));
end;					

1:
2:
3:
4:
5:
6:
7:
8:
9:
10:
11:
12:
13:
14:
15:
16:
17:

var
  a, b: TFoo;
  Test: TMemoryStream;
begin
  a := 'test';
  b := '12345';
  ShowMessage(a + b);
  Test := TMemoryStream.Create;
  try
    a.SaveToStream(Test);
    Test.Position := 0;
    b.LoadFromStream(Test);
    ShowMessage(b);
  finally
    Test.Free;
  end;
end;					

1:
2:
3:
4:
5:
6:
7:
8:
9:
10:
11:

var
  a: AnsiString;
begin
  a := ' ';
  PByte(@a[1])^ := $D8;
  PWord(LongInt(a) - 12)^ := 1251;
  ShowMessage(a);
  PWord(LongInt(a) - 12)^ := 1252;
  ShowMessage(a);
  PWord(LongInt(a) - 12)^ := 1253;
  ShowMessage(a);