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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: I am not understanding user defined exceptions
Date: Sat, 04 Feb 2017 08:41:30 +0000
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Xref: news.eternal-september.org comp.lang.ada:33239
Date: 2017-02-04T08:41:30+00:00
List-Id: <comp.lang.ada>

You are thinking of user-defined *predicates* (properties of values of
the type), available in Ada2012.

Try

   subtype Not_One is Integer with Dynamic_Predicate => Not_One /= 1;
   X : Not_One;

(with GNAT, you have to enable assertion checking, compile with -gnata)

   $ ./test_exceptions 
   2
   1

   raised SYSTEM.ASSERTIONS.ASSERT_FAILURE : Dynamic_Predicate failed at
   test_exceptions.adb:9

(line 9 is the second Get)