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From: tchrist@convex.COM (Tom Christiansen)
Newsgroups: comp.lang.perl
Subject: Re: $# question
Message-ID: <108982@convex.convex.com>
Date: 19 Nov 90 23:05:29 GMT
References: <LTaVs1w163w@cybrspc>
Sender: news@convex.com
Reply-To: tchrist@convex.COM (Tom Christiansen)
Organization: CONVEX Software Development, Richardson, TX
Lines: 54

In article <LTaVs1w163w@cybrspc> roy%cybrspc@cs.umn.edu (Roy M. Silvernail) writes:
>I'm a little confused about a detail regarding $#...
>
>Wouldn't $# make more sense if it were to
>point to the array element _past_ the last element assigned? (i.e. to
>the null element past '5' in the above example) Then it could be used
>directly as an indication of size, and as well, you could do
>
>while (<instream>) {
>        @foo[$#foo] = $_;
>}
>
>to fill an array with an incoming stream of fields. (using @foo[$#foo +1]
>works, but it's less intuitive to me)

It's also wrong -- you're using @ for $, which is a no-no, and tended
to coredump earlier version of perl.  I used to get bug reports on this
one from my users all the time.  Remember: when you want ONE value, 
use a $, and when you want many, use an @, as in:

    print $foo[1];
    print @foo[1..3];



Anyway, while you could have written the above as:

    while (<INSTREAM>) {
	$foo[++$#foo] = $_;
    }

That's not idiomatic perl.  In <8225@jpl-devvax.JPL.NASA.GOV> Larry
wrote: (yes, I do collect these.)

    Whenever you see subscripts in a Perl script, it's a pretty strong
    indication that things aren't being done the Perl Way.

A cheaper way way to do this in perl would be

    while (<INSTREAM>) {
	push(@a, $_);
    }

This runs in 70% the time of the previous example on my machine.

This is nearly as fast as

    @a = <INSTREAM>;

Which runs in 65% of the original time.  Of course, you may not
want to do this on small-memory machines and/or big files.


--tom