Re: slice'access?

[dewar@gnat.com (Robert Dewar)]

tmoran@acm.org wrote in message news:<1KGH8.384$9_7.69072060@newssvr13.news.prodigy.com>...
> Is there a nice way to create an access to a slice? eg

> type p is access all string;
> s : aliased string:="12345";
> ptr : p := s'access; -- OK
> ptr : p := s(2 .. 4)'access; -- ??


The answer of course is no. The RM does not allow this
and if you think for just a moment it is obvious why. The
usual representation of bounds for an array is to have the
bounds immediately before the data, but of course that
would be incompatible with allowing access of a slice.
So to allow this would be a huge earthquake for most
compilers.

Now in GNAT, fat pointers allow separation of the data
and the bounds, so GNAT can accomodate this. Of course
it cannot allow the clearly illegal construction above,
but if you use 'unrestricted_access then the above code
is valid in GNAT. Of course if you use a compiler that 
does not implement the Unrestricted_Access attribute,
you are out of luck.