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From: Keean Schupke <keean.schupke@googlemail.com>
Newsgroups: comp.lang.ada
Subject: Re: Efficient Sequential Access to Arrays
Date: Thu, 26 Jul 2012 05:32:32 -0700 (PDT)
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Date: 2012-07-26T05:32:32-07:00
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On Thursday, 26 July 2012 11:10:39 UTC+1, Brian Drummond  wrote:
> On Thu, 26 Jul 2012 01:38:41 -0700, Keean Schupke wrote:
> 
> &gt; This is an equivalent concept to nullable, so two questions:
> &gt; 
> &gt; What is the literal for &#39;invalid&#39;, IE:
> &gt; 
> &gt; X : Index := #INVALID -- we should be able to initialise to invalid.
> &gt; 
> &gt; if X = #INVALID -- I want to be able to test for invalid.
> 
> There&#39;s an attribute for that.
> 
> if X&#39;Valid ...
> 
> - Brian


So if I do

if X'Valid then
    Y(X) -- if X is the same type as the index of Y then no need to range check.
end if

If I explicitly check 'Valid, the compiler should be able to omit some implicit range checks, as 'Valid is an explicit range check.


Cheers,
Keean.