Re: How to hide instantiation of Direct_IO?

["Norman H. Cohen" <ncohen@watson.ibm.com>]

Dale Stanbrough wrote:
> 
> I'ld like to develop a package on top of the rather low level Direct_IO,
> but prevent access to the instantiation of Direct_IO itself.
> 
> I could do this by instantiating direct_io in a private part of a
> package, and then declare higher level routines in child packages which
> for the most part, simply forward the work onto the equivalent direct_io
> routines.
> 
> However there seems no way to declare a type Count for my higher level
> package such that it has the same range as that defined in Direct_IO
> (type Count is 0..implementation-defined) - I can't reference the
> private instantiation - 'cos it's private!

This is one of those relatively unusual occasions on which one misses
the ability to interleave private and public declarations, as in C++.

Why not declare an integer type with the maximal range, i.e., 

   type Count is range 0 .. System.Max_Int;

and use that?  (One drawback is that your equivalent of Set_Index will
have to include a run-time check for an index that is larger than the
underlying machinery can handle, i.e., larger than Count'Last, but there
are already such run-time checks for the file-index values passed to the
Direct_IO procedures Read and Write, as described in RM A.8.5(4) and
A.8.5(7).)

-- 
Norman H. Cohen
mailto:ncohen@watson.ibm.com
http://www.research.ibm.com/people/n/ncohen