Passing by reference

28 Feb 2005

      Another problem, also reported on the macpascal mailing list and 
reproduced by the following program:

[G5:gcc/p/test] adriaan% cat avo12.pas
program avo12;

type
         Str255 = record sLength: Byte; sChars: packed array[1..255] of 
char; end;

  function StringToStr255 ( const s: String ) = Result : Str255;
   begin
     Result.sLength := Min( Length( s ), 255 );
     if Result.sLength > 0 then begin
       Result.sChars[1..Result.sLength] := s[1..Result.sLength];
     end;
   end;

procedure DrawString1( const s: Str255); external name 'DrawString';
procedure DrawString2( protected var s: Str255); external name 
'DrawString';

begin
         DrawString1( StringToStr255( 'Hello')); {OK}
         DrawString2( StringToStr255( 'Hello'))  {Error: reference 
expected, value given}
end.

[G5:gcc/p/test] adriaan% gpc avo12.pas
avo12.pas: In main program:
avo12.pas:19: error: reference expected, value given

In gpc-20030830, this was no problem, but now it is no longer allowed, 
which is quite inconvenient. In the GPC interfaces for Mac OS X, we use 
the external declaration form with a "protected var" because (according 
to the gc docs) the "const" declaration form doesn't guarantuee that 
the parameter is passed by reference, which is an ABI requirement.

Regards,

Adriaan van Os