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From: "J-P. Rosen" <rosen@adalog.fr>
Newsgroups: comp.lang.ada
Subject: Re: Inferring array index type from array object
Date: Wed, 23 Jun 2010 11:03:17 +0200
Organization: Adalog
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Date: 2010-06-23T11:03:17+02:00
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Dmitry A. Kazakov a �crit :
>> 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;
> 
> subtype Index_Span is Integer range S'Range;
> I : Index_Span := S'First;
Or simply:
I : Positive range S'Range;

>> 1. What is the standard justification for this assymetry?
This is a simplification of loops, to avoid some typing to the user.
Think of it the other way round: since a for loop involves the
declaration of an object, the type should always be explicitely declared
(a coding rule that I apply - of course checkable by AdaControl):

for I in positive range 1..10 loop ...
for I in positive range S'Range loop ...

So it is really symetrical, except that in the case of a loop, you  are
allowed to "simplify" by omitting the "<type> range" part - forcing the
compiler to deduce the type from the range, which is not a good idea IMHO.

>> 2. Is it possible to declare the index variable without hardcoding the
>> index type (that is, to infer it from the array object)?
> 
There is no point in doing this, since the type of the array /is/
hardcoded anyway. You could allow the same "simplification" as for
loops, but as mentionned above, I prefer the other way round: always
explicitely give the type name.

-- 
---------------------------------------------------------
           J-P. Rosen (rosen@adalog.fr)
Visit Adalog's web site at http://www.adalog.fr