Path: utzoo!attcan!uunet!ogicse!iwarp.intel.com!news
From: merlyn@iwarp.intel.com (Randal L. Schwartz)
Newsgroups: comp.lang.perl
Subject: Re: While learning PERL... a suggestion
Keywords: perl file learn suggest
Message-ID: <1991Jan24.100539.20366@iwarp.intel.com>
Date: 24 Jan 91 10:05:39 GMT
References: <1991Jan19.003519.23569@ux1.cso.uiuc.edu> <11115@jpl-devvax.JPL.NASA.GOV> <118879@uunet.UU.NET> <1991Jan21.092204.11944@ux1.cso.uiuc.edu> <1991Jan21.174520.12207@iwarp.intel.com> <1991Jan21.201845.28080@ux1.cso.uiuc.edu>
Sender: news@iwarp.intel.com
Reply-To: merlyn@iwarp.intel.com (Randal L. Schwartz)
Organization: Stonehenge; netaccess via Intel, Beaverton, Oregon, USA
Lines: 52
In-Reply-To: phil@ux1.cso.uiuc.edu (Phil Howard KA9WGN)

In article <1991Jan21.201845.28080@ux1.cso.uiuc.edu>, phil@ux1 (Phil Howard KA9WGN) writes:
| >You could also futz with the namespace, like:
| 
| >	*HANDLE = $filehandle[17];
| >	print HANDLE "this goes to the 17th filehandle";
| 
| >but remember that this affects &HANDLE, %HANDLE, and @HANDLE as well.
| >(I understand that this is more efficient than the indirect filehandle
| >if you do more than one I/O per filehandle switch.)
| 
| In what way does it affect them?  I was getting the impression from the
| man pages that these name spaces were separate.  This was discussed in
| the man pages with regard to passing by references, but I guess you are
| now filling in the ambiguities of its affect elswhere.  I'm not up on
| subroutines yet (probably mostly due to not understand how the name
| space works).

The name spaces are separate in the ordinary sense, but the * operator
is not an ordinary operator. :-)

I hope Larry will forgive me for the following.  It's probably close
enough for jazz, but Larry will cringe at the description.

Think of *FOO as the internal representation of the symbol "FOO" in
the program, in *whatever* form it is used: &FOO, $FOO, %FOO, @FOO,
and FOO as a filehandle.  When you say *BAR = *FOO, you are really
saying that BAR can be used anywhere that FOO can be used with
identical results.  It doesn't matter if there's an intermediate step:
you could say $a = *FOO then *BAR = $a.

So assigning something to *BAR _must_ affect all object with a BAR as
their name.  It's dangerous... it's not just for filehandles.

Now, the one little tricky that I didn't describe so far is what I
used in my previous post.  Namely: that *BAR = *FOO can also be
accomplished with *BAR = 'FOO', because Perl will look up FOO at
runtime to figure out what it really is.  Now, since the "name" FOO is
quoted, you could really stick anything there, like *BAR = '42*xx',
and now the name BAR is a synonym with another name 42*xx, even though
that sort of name would never make it past the parser.

There.  Clear as mud? :-)

By the way, I just got home from Uniforum.  It was great.  300 books
sold and signed within 2 hours.  My hand is tired. :-)

print do {{ redo unless "Just another Perl hacker,"; }} # huh? :-)
-- 
/=Randal L. Schwartz, Stonehenge Consulting Services (503)777-0095 ==========\
| on contract to Intel's iWarp project, Beaverton, Oregon, USA, Sol III      |
| merlyn@iwarp.intel.com ...!any-MX-mailer-like-uunet!iwarp.intel.com!merlyn |
\=Cute Quote: "Intel: putting the 'backward' in 'backward compatible'..."====/