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From: Peter N Lewis
Subject: Forward defined types (and object
Date: 7 Jul 2005, 19:55:20

At 12:32 +0200 7/7/05, Frank Heckenbach wrote:
>Peter N Lewis wrote:
>
>  > >Peter N Lewis wrote:
>>  >  > 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.
>
>This would be wrong, as pointer targets can (according to standard
>Pascal and all other dialects) be of any type and may be
>forward-referenced, e.g. in this example, b is probably not
>pointer-sized, but it must work:
>
>program Foo;
>
>type
>   a = ^b;
>   b = array [1 .. 1000] of Integer;

CW handles this as well.  So it handles the two cases, an unknown 
identifier, and forward pointer references (as in, an unknown 
identifier after ^)

The handling of unknown identifiers is for the other cases (other 
than ^unknown).

>Actually, I just tried to figure out what BP does. It seems to be
>buggy. `{$T+}' is supposed to enforce strict type-checking with the
>address operator (@), but in this case is seems to allow the wrong
>assignment, and reject the right one. Anyway, bar really seems to be
>a pointer to a reference, so it would not help us here.

I'm not sure about BP, but I know CW often requires the @ before a 
procedure name for an assignment to a procedural variable to remote 
the ambiguity of whether to call it or not - and then introduces the 
new ambiguity of whether it is a procedural pointer or a pointer to a 
procedure pointer.  Ie, in CW:

function doit( a: Integer ): Integer;
begin
   return 1;
end;
type proc = function ( a: Integer ) : Integer;
var a: proc;
begin
   a := @doit;
   WriteLn( a( 10 ) ); // prints 1
end;

Perhaps BP does something equally weird.

>  > >It requires the `class' keyword. There is a problem, that `class' keyword
>>  >is (ATM) not accepted in Mac Pascal mode. It would be easy to implement
>>  >syntax with `object' as an alternate keword,
>
>As Gale wrote, the Mac Pascal syntax seems to be `object; forward;'.
>So if you can add this without conflicts, this would be preferable,
>I think.

Any (or all) of the different syntax is fine by me.

>  > >but than we would have to decide
>>  >what to do if `object' is used in a forward declaration in one mode, but
>>  >the proper declaration uses different mode.
>
>This should be an error IMHO. Why should we allow such useless
>obscurities?

Agreed.  Indeed, I would think it would be an error to forward 
declare (or define after a forward declare) any non-reference object.

Enjoy,
    Peter.

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