----boundary-LibPST-iamunique-1987502256_-_-
Content-type: text/plain
Dear Wojtek,
This is certainly not a bug.
One cannot change the signutare in the overriding method
except by narrowing the receiver type and the function result type.
Stores.Store is a pointer, and In/Externalize are defined with
the pointer as receiver, so one cannot use a VAR record there.
Perhaps if the language now allows one to define
a pointer type extending a record type and vice versa,
it might be logical that it should be allowed
to use either pointer or a variable as the receiver.
But perhaps there are hidden obstacles for that?
Cheers
Fyodor Tkachov
>
> Hello:
>
> here is a short module which does not compile, what looks strange.
> The PT is an extension of Stores.Store. It is a record, not a pointer
> to record. The language report says that it should be allowed, and
> the compiler does not complain about the PT declaration.
>
> The PPT is also an extension of Stores.Store, but this time it is a
> pointer. This is also allowed.
>
> The following citation from the Language Manual suggests that all is fine.
> The base type can be a RECORD or alternatively a pointer. I infer that
> both the PT and PPT declarations are just fine, and the compiler thinks
> the same.
> > Alternatively, a pointer type can be specified as the base type. The
> > record base type of the pointer is used as the base type of the declared
> > record in this case.
>
> So, why does not the following module compile? Excuse me if the answer is
> obvious. I somehow cannot figure this out.
>
> MODULE DanomTest;
> IMPORT Stores, Dialog;
> TYPE
> PT* = RECORD (Stores.Store)
> tree*: Dialog.Tree
> END;
> PPT* = POINTER TO RECORD (Stores.Store)
> tree*: Dialog.Tree
> END;
>
> (*compile error "parameter does not match"*)
> PROCEDURE (VAR pt: PT) Internalize-(VAR rd: Stores.Reader);
> BEGIN (*Internalize*)
> END Internalize;
>
> (*compile error "parameter does not match"*)
> PROCEDURE (VAR pt: PT) Externalize-(VAR wr: Stores.Writer);
> BEGIN (*Externalize*)
> END Externalize;
>
> (*no error*)
> PROCEDURE (ppt: PPT) Internalize-(VAR rd: Stores.Reader);
> BEGIN (*Internalize*)
> END Internalize;
>
> (*no error*)
> PROCEDURE (ppt: PPT) Externalize-(VAR wr: Stores.Writer);
> BEGIN (*Externalize*)
> END Externalize;
>
> END DanomTest.
>
>
>
> Wojtek Skulski skulski{([at]})nowhere.xy>
> --------------------------------------------
>
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----boundary-LibPST-iamunique-1987502256_-_-
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----boundary-LibPST-iamunique-1987502256_-_---
Received on Wed Jul 02 2003 - 01:11:41 UTC