Re: class wide object in generic package

[Stephen Leake <stephen_leake@acm.org>]

Thomas Maier-Komor <maierkom@rcs.ei.tum.de> writes:

> Hi everybody,
> 
> I am getting this error message when compiling the
> code at the end of the message:
> 
> generic_pac.adb:7:26: class-wide argument not allowed here
> generic_pac.adb:7:26: "eval" is not a primitive operation of "Object"
> 
> 
> my question is:
> first: is it possible to declare a procedure in the
> generic part so that it will be a primitive operation of
> Object?

No. All primitive operations are declared in the same declarative
region as the type.

> second: why isn't a class-wide argument not allowed in this place?

Because "eval" isn't a primitive operation of Object :). Using a
class-wide argument means you _want_ dispatching. Only primitive
operations can be dispatching.

You have a couple choices to make this work. If you don't actually
need dispatching, you can make eval take a class-wide argument:

with procedure eval(o : in out Object'class);

If you want dispatching, you'll have to use a generic formal package
parameter:

generic
   package Object_Package is new Generic_Obj_Package (...);
package generic_pac ...

Then in Generic_Obj_Package, declare Object and Eval. Note that it has
to be generic!

Good luck,

-- 
-- Stephe