delphi - How do I use class helpers to access strict private members of a class?

Question

This is a follow-up question to: How to hide a protected procedure of an object?
(I'm a bit fuzzy on the whole class helper concept)

Suppose I have an class like:

type 
TShy = class(TObject) 
strict private
  procedure TopSecret;
private
  procedure DirtyLaundry;  
protected 
  procedure ResistantToChange;
end; 

I know I can access the private method if I have the source code by adding a descendent class in the same unit.

I have 2 questions:
- How do I employ a class helper to access the strict private member?
- Can I use a class helper in a separate unit to access (strict) private members?

Answer 1

Up to, and including Delphi 10.0 Seattle, you can use a class helper to access strict protected and strict private members, like this:

unit Shy;

interface

type
  TShy = class(TObject)
  strict private
    procedure TopSecret;
  private
    procedure DirtyLaundry;
  protected
    procedure ResistantToChange;
  end;

unit NotShy;

interface

uses
  Shy;

type
  TNotShy = class helper for TShy
  public
    procedure LetMeIn;
  end;

implementation

procedure TNotShy.LetMeIn;
begin
  Self.TopSecret;
  Self.DirtyLaundry;
  Self.ResistantToChange;
end;

end.

uses
  ..., Shy, NotShy;

procedure TestShy;
var
  Shy: TShy;
begin
  Shy := TShy.Create;
  Shy.LetMeIn;
  Shy.Free;
end;

However, starting with Delphi 10.1 Berlin, this no longer works! Class helpers can no longer access strict protected, strict private or private members. This "feature" was actually a compiler bug that Embarcadero has now fixed in Berlin. You are out of luck.