Forward defined types (and object references)

[Peter N Lewis]

At 9:07 +0200 6/7/05, Marco van de Voort wrote:
>  > marcov at stack.nl wrote:
>
>>  > Delphi supports this: (remember its object model is similar)
>>  >
>>  > Type
>  > >     MyObjectB = class;
>  > >     MyObjectA = class;
>>
>>  This seems to be what `class .. end' is in OOE.
>>
>>  > Must be in one typeblock though, IOW, the same system as pointers.
>>
>>  Yes, same in OOE.
>
>Does CW work like OOE in this regard?

No, CW does not accept either syntax:

MyObject = object;
nor
MyObject = object .. end;

CW takes the approach that any unknown type identifier it sees in a 
type definition is pointer sized (a pointer or object) and must be 
defined by the end of the type block.

   type
     rec = record
       a: UndefinedA;
       b: UndefinedB;
     end;
     UndefinedA = ^Integer;
     UndefinedB = object
     end;

Note that UndefinedA = UInt32 is not legal, it must be a pointer or object.

It's actually not a bad methodology and makes it easy to write data 
structures that is self or mutually referential, but it does not add 
anything over pre defining pointers or object names as EP/Delphi.

>Note that afaik there is no solution for BP style objects, and actually you
>don't really need it, since in practice you always work with references
>(explicit pointers).

There is still this case:

type
   proc = procedure ( var o: MyObject );
   MyObject = object
     f: proc;
   end;

But I agree, in practice with non-reference objects, the issue is a 
lot less prevalent.

Enjoy,
    Peter.

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