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From: davidm@rational.com (David Moore)
Newsgroups: comp.lang.ada
Subject: Re: Ada95 and Dynamic Type Identification
Date: 18 Jan 1995 17:33:22 GMT
Organization: Rational Software Corporation
Message-ID: <3fjjd2$e87@rational.rational.com>
References: <milodD2Ko8z.98w@netcom.com>
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Date: 1995-01-18T17:33:22+00:00
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milod@netcom.com (John DiCamillo) writes:


>Does Ada95 have some sort of dynamic type identification
>equivalent to C++ RTTI or Eiffel's assignment-attempt?
>That is, given a procedure

>   procedure Process_Alerts(A: Alert'Class) ...

>Is there any way to find out precisely what type of
>object A is?  Or are we limited to dynamic dispatch?

There is an attribute "tag". So if we want to determine if
A is of a particular type (Dozing, say) we can either write:

if a'tag=dozing'tag then

or we can write:

if a in dozing then

There is also a predefined package that will return textual names
of types. 

package ada.tags is
   type tag is private;
   function expanded_name(t:tag) return string;
   function external_tag(t:tag) return string;
   function internal_tag(external:string) return tag;
private 
...
end ada.tags;

Note we can also say

if a in dozing'class

which will be true if a is in any class derived from the tagged type.