[Lazarus] Forward declare (modern) records [was: Re: "global" operator overloading]

[Sven Barth]

On 26.02.2013 18:22, Jürgen Hestermann wrote:
>
> Am 2013-02-26 16:15, schrieb ListMember:
>>
>> Is it possible to forward declare records the way we can with classes?
>>
>
> Well, I know that you can do something like this:
>
>       PTreeType    = ^TreeType;
>       TreeType   = record
>                              ...;
>                              ...;
>                              Dirs : PListType;
>                              end; { of record }
>
> You can see that "TreeType" is used in the first line although it is not
> (yet) defined.
> As long as you declare the type within the same "Type" section the
> compiler swallows it.

He wants to have this supported:

=== example begin ===

type
   SomeType1 = record;
   SomeType2 = record;

   SomeType1 = record
     // ...
     property SomeProperty: SomeType2 read ... write ...
   end;

   SomeType2 = record
     // ...
     property SomeProperty: SomeType1 read ... write ...
   end;

=== example end ===

Just in case you aren't up to date with FPC's supported language, 
Jurgen, the following works in FPC out of Delphi compatibility since 
2.6.0 (though it needs {$modeswitch advancedrecords} in non-Delphi modes):

=== example begin ===

type
   SomeType = record
     // ...
     property SomeProperty: SomeType read ... write ...
   end;

=== example end ===

What still doesn't work (and will never work [and doesn't work in Delphi 
either :P ]) is this:

=== example begin ===

type
   SomeType = record
     SomeField: SomeType;
   end;

=== example end ===

Regards,
Sven