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From: jls@yoda.Rational.COM (Jim Showalter)
Newsgroups: comp.lang.ada
Subject: Re: procedural variables
Message-ID: <jls.666836939@yoda>
Date: 18 Feb 91 00:28:59 GMT
References: <9102110959.aa23851@PARIS.ICS.UCI.EDU> <662@esosun.UUCP> <24590@neptune.inf.ethz.ch> <2834@cod.NOSC.MIL>
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>>Could anybody explain what the rationale for not including procedural
>>variables in Ada is (I have heard it has been discussed and dismissed again
>>in the past few years) ?

They were deemed unsafe, because it is possible to get all fouled up
with lifetime issues. Consider this example:

    procedure outer (...) is

        type some_procedure_type is ...

        foo : some_procedure_type;

        procedure middle (...) is
        
            procedure short_lifetime (...) is -- MATCHES some_procedure_type
            begin
                ...
            end short_lifetime;

        begin
            foo := short_lifetime;
        end middle;

    begin
        middle (...);
        foo; -- WHAT SHOULD HAPPEN HERE?
    end outer;

Anyway, 9x looks like it will have these puppies. How they get around
problems like the above I don't know--I suggest raising program_error
whenever it occurs.
--
***** DISCLAIMER: The opinions expressed herein are my own. Duh. Like you'd
ever be able to find a company (or, for that matter, very many people) with
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                   -- "When I want your opinion, I'll beat it out of you."