[fpc-pascal] private type and type compatibility

[Sven Barth]

Am 30.10.2013 12:06, schrieb Frederic Da Vitoria:
> 2013/10/30 Jonas Maebe <jonas.maebe at elis.ugent.be 
> <mailto:jonas.maebe at elis.ugent.be>>
>
>     On 30 Oct 2013, at 10:36, Michael Van Canneyt wrote:
>
>         I think it is an error. You declare something as private, and
>         then you use it in a public function ? If that is not a
>         visibility clash, I don't know what is :)
>
>
>     The ability to use types in public functions that are not
>     necessarily visible to users of that function is quite common in
>     Pascal. Otherwise, for consistency you would also have to give a
>     compile time error when compiling this:
>
>     unit u1;
>
>     interface
>
>     type
>       tdynarray = array of integer;
>
>     implementation
>
>     end.
>     *********
>
>     unit u2;
>
>     interface
>
>     uses
>       u1;
>
>     function f: tdynarray;
>
>     implementation
>
>     function f: tdynarray;
>     begin
>     end;
>
>     end.
>     **********
>
>     program test;
>
>     uses
>       u2;
>
>     var
>       a: array of integer;
>     begin
>       a:=f;
>     end.
>     ***
>
>     The tdynarray type is not visible in the program because u1 is not
>     in its uses clause (it's not in scope whatsoever), and
>     nevertheless there is no problem to use it. It's of course not
>     exactly the same (tdynarray isn't declared as private to u1), but
>     at the scope visibility level it is the same situation as far as I
>     am concerned.
>
>
> Precisely, shouldn't this trigger an error too? The code should not be 
> able to reference anything for which the declaration isn't visible, 
> isn't it?
But the compiler can not know whether the user of unit u2 has unit u1 in 
scope or not.

Regards,
Sven
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