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From: Jeffrey Carter <spam.jrcarter.not@spam.not.acm.org>
Newsgroups: comp.lang.ada
Subject: Re: "NULL" returned by a function
Date: Fri, 08 Aug 2014 14:19:13 -0700
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Date: 2014-08-08T14:19:13-07:00
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On 08/08/2014 02:10 PM, Victor Porton wrote:
> What if I want to make a function which returns either a value of type T or
> a value signifying "nothing" (like null pointer)?

Typically one should use a variant record with one variant for "nothing" and 
another for the value:

type Result (Has_Value : Boolean := False) is record
    case Has_Value is
    when False =>
       null;
    when True =>
       Value : T;
    end case;
end record;

-- 
Jeff Carter
"We call your door-opening request a silly thing."
Monty Python & the Holy Grail
17