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From: eachus@spectre.mitre.org (Robert I. Eachus)
Newsgroups: comp.lang.ada
Subject: Re: Change to obscure visibility rule in 9x
Followup-To: comp.lang.ada
Date: 18 Oct 94 15:23:06
Organization: The Mitre Corp., Bedford, MA.
Message-ID: <EACHUS.94Oct18152306@spectre.mitre.org>
References: <GRAHAM.94Oct18094458@clsi.clsi.COM>
NNTP-Posting-Host: spectre.mitre.org
In-reply-to: graham@clsi.COM's message of 18 Oct 1994 13:44:58 GMT
Date: 1994-10-18T15:23:06+00:00
List-Id: <comp.lang.ada>


    You seem to be right.  I just reread RM9X5.0, and the wording
changes seem to have lost this detail.  ("A declaration" is hidden,
not "all declarations."

    Now as to why.  During the declaration of a subprogram, its
parameter and result profile cannot be determined, in other
declarations similar things happen.  So to avoid requiring compilers
to do handsprings to determine whether or not a particular declaration
with the same name is hidden, they all are.

    But why "neither by selection nor directly"?  Because you can have
qualified names that name the current declaration or a component of
it.  How do you know whether or not the current unit is a (possible)
match of the qualified name?  Again, it is a nasty recursion, and
since it is also bad programming, the easiest rule is to make all the
problem cases illegal.

    There are a few cases which are considered stylisticly acceptable,
and the rules specifically allow such constructs as:

     package Float_IO is new Text_IO.Float_IO;
     procedure Reset renames Very_Long_Package_Name.Reset;

--

					Robert I. Eachus

with Standard_Disclaimer;
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function Message (Text: in Clever_Ideas) return Better_Ideas is...