[fpc-devel] Allow record helper inheritance in Delphi mode

[Ondrej Pokorny]

On 29.08.2017 11:48, Sven Barth via fpc-devel wrote:
> The idea is okay as well, but I'd name it RecordHelperInheritance, 
> cause if we'd allow "type helper" in mode Delphi (as Maciej asks) then 
> those would support inheritance by default as they aren't Delphi 
> compatible as a whole anyway.

Actually, IMO {$modeswitch typehelpers} should be supported in delphi 
mode as well - just like {$modeswitch advancedrecords} is. Some code to 
test:

program Project1;

{$mode delphi}
{$modeswitch typehelpers+} // it doesn't allow "TStringHelper = type 
helper for AnsiString"
{$modeswitch advancedrecords-} // it doesn't disable record helper for TRec

type
   TRec = record
     A, B: Integer;
   end;

   TRecHelper = record helper for TRec
   public
   end;

   TStringHelper = type helper for AnsiString
   public
   end;

begin
end.

Furthermore the record helper Delphi syntax is supported in ObjFPC mode 
- even with inheritance [!]:

program Project1;

{$mode objfpc}
{$modeswitch typehelpers+}
{$modeswitch advancedrecords}

type
   TRec = record
     A, B: Integer;
   end;

   TRecHelper = record helper for TRec
   public
   end;

   TStringHelper = record helper for AnsiString
   public
     function R: string;
   end;

   TStringHelper2 = record helper(TStringHelper) for AnsiString
   public
     function R2: string;
   end;

function TStringHelper2.R2: string;
begin
   Result := 'R2';
end;

function TStringHelper.R: string;
begin
   Result := 'R';
end;

var
   S: AnsiString;
begin
   Writeln(S.R2);
end.


So, yes. There are inconsistencies that should be fixed:
1.) Support {$modeswitch typehelpers +/-} in delphi mode.
2.) Add a new modeswitch "RecordHelperInheritance" to enable/disable 
record helper inheritance in all modes.

Ondrej