Inferring array index type from array object

[Maciej Sobczak <see.my.homepage@gmail.com>]

Consider this:

S : String := "Hello";

It is possible to iterate over all indices of this array with this
construct:

for I in S'Range loop ...

I would like to declare I as a free variable instead and I would
expect some symmetry in the language by doing this:

I : S'Range := S'First;

But it does not work. Of course, one can do:

I : Positive := S'First;

But it has the disadvantage of hardcoding the index type and
introducing unnecessary coupling in the code.
(hint: the problem is not really about Strings, it is a general array
question)

I have two questions:

1. What is the standard justification for this assymetry? What exactly
makes S'Range "work" in a for loop?

2. Is it possible to declare the index variable without hardcoding the
index type (that is, to infer it from the array object)?

--
Maciej Sobczak * http://www.inspirel.com

YAMI4 - Messaging Solution for Distributed Systems
http://www.inspirel.com/yami4