[32937] in Perl-Users-Digest
Perl-Users Digest, Issue: 4213 Volume: 11
daemon@ATHENA.MIT.EDU (Perl-Users Digest)
Thu May 15 11:09:19 2014
Date: Thu, 15 May 2014 08:09:03 -0700 (PDT)
From: Perl-Users Digest <Perl-Users-Request@ruby.OCE.ORST.EDU>
To: Perl-Users@ruby.OCE.ORST.EDU (Perl-Users Digest)
Perl-Users Digest Thu, 15 May 2014 Volume: 11 Number: 4213
Today's topics:
Re: Help with an operator precedence (?) puzzle <rweikusat@mobileactivedefense.com>
Re: Help with an operator precedence (?) puzzle <rweikusat@mobileactivedefense.com>
Re: Help with an operator precedence (?) puzzle <news@lawshouse.org>
Digest Administrivia (Last modified: 6 Apr 01) (Perl-Users-Digest Admin)
----------------------------------------------------------------------
Date: Thu, 15 May 2014 15:11:15 +0100
From: Rainer Weikusat <rweikusat@mobileactivedefense.com>
Subject: Re: Help with an operator precedence (?) puzzle
Message-Id: <87k39nnncs.fsf@sable.mobileactivedefense.com>
Henry Law <news@lawshouse.org> writes:
> Perl 5.14 running on Ubuntu. I'm fairly sure that the answer to this
> is operator precedence but I've looked at it and consulted perldoc
> until my brain hurts and I can't work it out. Could someone explain?
[...]
> #!/usr/bin/perl
> use strict;
> use warnings;
> use 5.010;
>
> sub tryit {
> my ( $user, $conf, $parms ) = @_;
> $@ = "reset_user: invalid parameters\n" and return if $parms==1;
> $@ = "reset_user: '$user' doesn't exist\n" and return if $parms==2;
> }
>
> If I compile it Perl warns me: "Found = in conditional, should be ==
> at tryout.pl line 8."
$parms == 1 and $@ = "reset toastbrot" and return;
The second and-junctor is technically nonsense because the value
of its left-hand operand will always be true. The perl compiler was so
kind to assume that you meant to write something sensible and
accidentally forgot to put in the == which would have turned this into a
(still rather bizarre) test.
The easy way to avoid being told than one isn't making sense by a
computer is to stop confusing it (and the hypothetical maintencance
programmer would be very grateful for that), ie, use
sub tryit {
my ( $user, $conf, $parms ) = @_;
$@ = "reset_user: invalid parameters\n", return if $parms==1;
$@ = "reset_user: '$user' doesn't exist\n", return if $parms==2;
}
instead.
NB: 'Mr Law' is unlikely to see this but I hope it may be useful for
someone else. Usually, I wouldn't write it in this style ...
------------------------------
Date: Thu, 15 May 2014 15:20:57 +0100
From: Rainer Weikusat <rweikusat@mobileactivedefense.com>
Subject: Re: Help with an operator precedence (?) puzzle
Message-Id: <87fvkbnmwm.fsf@sable.mobileactivedefense.com>
tmcd@panix.com (Tim McDaniel) writes:
> In article <mM2dna38mqJp2ezOnZ2dnUVZ8rOdnZ2d@giganews.com>,
> Henry Law <news@lawshouse.org> wrote:
[...]
>>But line 9 is virtually identical, except for the presence of an
>>interpolated variable, and it compiles clean! Blowed if I know why.
>
> At a guess, the "Found = in conditional" warning is a heuristic that
> gets confused somehow by an interpolated string in particular. That
> is, it's the lack of a message line 9 that is the problematic one, not
> line 8.
This warning is produced by a routine named S_scalarboolean (op.c) and
it warns if it encounters a scalar assignment whose right operand is a
constant (in boolean context).
------------------------------
Date: Thu, 15 May 2014 15:55:12 +0100
From: Henry Law <news@lawshouse.org>
Subject: Re: Help with an operator precedence (?) puzzle
Message-Id: <Nf-dnQjud5LPSOnOnZ2dnUVZ7tednZ2d@giganews.com>
On 15/05/14 15:11, Rainer Weikusat wrote:
> NB: 'Mr Law' is unlikely to see this but I hope it may be useful for
> someone else. Usually, I wouldn't write it in this style ...
Eh? Phwatttt? What on earth makes you say that, I wonder.
The other stuff you wrote, of which I read every word, was helpful.
--
Henry Law Manchester, England
------------------------------
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Subject: Digest Administrivia (Last modified: 6 Apr 01)
Message-Id: <null>
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End of Perl-Users Digest V11 Issue 4213
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