Re: Generic default parameters

[Thomas Wolf <t_wolf@angelfire.com>]

stephen.a.leake.1@gsfc.nasa.gov wrote:
> Thomas Wolf <t_wolf@angelfire.com> writes:
> 
> > 5. Linked to (3) above: some way to specify a storage pool that
> >    is equal to whatever pool the compiler would use if no
> >    "for Some_Access'Storage_Pool use ..." clause was present, i.e.
> >    a generic way to refer to the standard storage pool of a type
> >    without referring to the type.

[...]

> I think a cleaner solution to 5 is a standard name for the standard
> storage pool, combined with 3 (default object for "in out"). So we'd
> have:
> 
>   generic
>      type Something is private;
>      Pool : in out System.Storage_Pools.Root_Storage_Pool'Class := 
>          System.Storage_Pools.Default_Storage_Pool;
>   package X is
>      type Some_Access is access all Something;
>      for Some_Access'Storage_Pool use Pool;
> 
> There may have to be more than one default storage pool; that may be
> why there is no standard name now.

Exactly. Every access type may have its own "standard" pool as far as I
can tell from the RM. Hence maybe something like your
System.Storage_Pools.Default_Storage_Pool, but it would need to be
treated specially: it'd have to denote not *one* particular pool,
but would have to denote depending on context *the* pool from the
set of all possible standard pools that would apply to a given access
type. Hmm... what about other uses of storage pools? It appears that
besides passing it around to finally assign it to some access type
with a representation clause one cannot do very much with a storage
pool, see RM 13.11(20).

While I still think something like that would be useful, I'm not sure
I like such a context dependent semantics...

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Thomas Wolf                          e-mail: t_wolf@angelfire.com