Can I define record helper for TBytes?

Question

I am using Delphi XE4. I try to define some helper function for TBytes:

TBytesHelper = record helper for TBytes
public
  function GetLength: integer;
end;

function TBytesHelper.GetLength: integer;
begin
  Result := System.Length(Self);
end;

When I try to consume the new helper function:

var B: TBytes;
    i: integer;
begin
  B := TBytes.Create(1,2,3);
  i := B.GetLength;

  if i <> Length(B) then
    raise Exception.Create('Incorrect result');
end;

I except the result for i is 3 but it doesn't. I refer to TStringHelper define in SysUtils.pas that has similar construct.

Is there anything I miss?

Answer 1

This problem was discussed here: https://forums.embarcadero.com/thread.jspa?threadID=88409 In few words - you can define your own type and use it with record helper:

type
 TMyBytes = array of Byte;

 TBytesHelper = record helper for TMyBytes
   function GetLength: integer;
 end; 

But it doesn't work with TBytes defined in Delphi. Support of helpers for generic types was added recently, so probably it is kind of limitations of current implementation.