Re: Generic formal access types

[mheaney@on2.com (Matthew Heaney)]

Robert A Duff <bobduff@shell01.TheWorld.com> wrote in message news:<wccof2lqoad.fsf@shell01.TheWorld.com>...
> 
> That works only if you want to declare the pointer type at the same
> place where the instantiation is.  In many cases, you don't.  For this
> reason, it's almost always better to pass the pointer type into
> generics.

That is indeed how the Charles library works wrt the Generic_Element
function: the client has to supply the access type.

To ensure complete generality for a reuseable component, passing in
the access type is the correct choice, since in many cases the client
already has an access type that goes with the designated type.

http://home.earthlink.net/~matthewjheaney/charles/


 
> When I invented the Address_To_Access_Conversions package (see chap 13),
> I made the mistake of declaring the pointer type inside the generic,
> because I thought the primary use would be peek/poke functionality, so
> you would always say ".all" right away.  And it makes the instantiation
> simpler.  But it turns out to be a pain.

I think a bigger problem is that the declared pointer type doesn't
turn off the storage pool.  If the designated type is T'Class, doesn't
this drag a lot of extra run-time baggage?

If you're converting from Address to Object_Pointer, then there's no
storage pool anyway, so it never made sense to me to give
Object_Pointer a storage pool.

 
> The "right" solution to the OP's problem is to pass in the designated
> type and the pointer type.  Yes, that requires an extra line of code at
> the instantiation.  But I don't think there's a better solution.

Yes.