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From: beckwb@ois.com (R. William Beckwith)
Newsgroups: comp.lang.ada
Subject: Re: Ada95 and Dynamic Type Identification
Date: 18 Jan 1995 14:12:17 -0500
Organization: Objective Interface Systems, Inc.
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Date: 1995-01-18T14:12:17-05:00
List-Id: <comp.lang.ada>

John DiCamillo (milod@netcom.com) wrote:

: 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?

: e.g.:

:       foo: FooAlert;         -- special alert
:    begin
:       foo ?= A;              -- is A a FooAlert?
:       if (foo'Valid) then    -- A IS a FooAlert!
:          FooHandler( foo );  -- do something that only
:                              -- applies to FooAlerts

4.5.2 Relational Operators and Membership Tests

    if A in FooAlert'CLASS then       -- is A a FooAlert?
       FooHandler(FooAlert'CLASS(A)); -- do something that only
    end if;                           -- applies to FooAlerts

The FooAlert'CLASS(A) type conversion is thus guaranteed
to work.

: Anyway, if dynamic typing was left out of Ada95, would 
: that be considered a mistake. Every other statically
: typed OOPL I know of has eventually provided some form
: of dynamic typing.  Why not Ada?  Is there some subtlety
: about Ada's type system that makes dynamic typing un-
: necessary or irrelevant?

Yes, leaving dynamic typing would have been a mistake.
I'm sure glad Ada95 has such a nice dynamic typing system.

... Bill