[25993] in Perl-Users-Digest
Perl-Users Digest, Issue: 8212 Volume: 10
daemon@ATHENA.MIT.EDU (Perl-Users Digest)
Wed Jun 29 03:05:23 2005
Date: Wed, 29 Jun 2005 00:05:07 -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 Wed, 29 Jun 2005 Volume: 10 Number: 8212
Today's topics:
What does +FOO mean? <BLOCKSPAMfishfry@your-mailbox.com>
Re: What does +FOO mean? <john@castleamber.com>
Re: What does +FOO mean? <tassilo.von.parseval@rwth-aachen.de>
Re: What does +FOO mean? <tadmc@augustmail.com>
Digest Administrivia (Last modified: 6 Apr 01) (Perl-Users-Digest Admin)
----------------------------------------------------------------------
Date: Tue, 28 Jun 2005 21:03:20 -0700
From: fishfry <BLOCKSPAMfishfry@your-mailbox.com>
Subject: What does +FOO mean?
Message-Id: <BLOCKSPAMfishfry-7FB93D.21032028062005@comcast.dca.giganews.com>
I'm looking at a lot of code where they have
use constant FOO => "foo";
and then later
my $hash{+FOO} ...
Can someone please explain what '+' signifies in this context?
------------------------------
Date: 29 Jun 2005 04:08:07 GMT
From: John Bokma <john@castleamber.com>
Subject: Re: What does +FOO mean?
Message-Id: <Xns9683EB156FA51castleamber@130.133.1.4>
fishfry <BLOCKSPAMfishfry@your-mailbox.com> wrote:
> I'm looking at a lot of code where they have
>
> use constant FOO => "foo";
>
> and then later
>
> my $hash{+FOO} ...
>
> Can someone please explain what '+' signifies in this context?
$hash{FOO} is $hash{'FOO'}
$hash{+FOO} is $hash{"foo"}
--
John Small Perl scripts: http://johnbokma.com/perl/
Perl programmer available: http://castleamber.com/
Happy Customers: http://castleamber.com/testimonials.html
------------------------------
Date: Wed, 29 Jun 2005 07:09:55 +0200
From: "Tassilo v. Parseval" <tassilo.von.parseval@rwth-aachen.de>
Subject: Re: What does +FOO mean?
Message-Id: <slrndc4b93.qu.tassilo.von.parseval@localhost.localdomain>
Also sprach fishfry:
> I'm looking at a lot of code where they have
>
> use constant FOO => "foo";
>
> and then later
>
> my $hash{+FOO} ...
>
> Can someone please explain what '+' signifies in this context?
Barewords in hash subscripts are treated by perl as strings. By writing
'{+FOO}' the subscript no longer qualifies as bareword and the Perl
interpreter then knows it is referring to an identifier, the constant
FOO.
Other ways to resolve this would be:
$hash{FOO()}
$hash{&FOO}
This works because under the hood constants are inlineable functions
(that is: functions with an empty prototype created at compile-time).
By the way:
my $hash{+FOO} ...
is a syntax-error. You cannot declare hash-elements with 'my'.
Tassilo
--
use bigint;
$n=71423350343770280161397026330337371139054411854220053437565440;
$m=-8,;;$_=$n&(0xff)<<$m,,$_>>=$m,,print+chr,,while(($m+=8)<=200);
------------------------------
Date: Wed, 29 Jun 2005 00:23:19 -0500
From: Tad McClellan <tadmc@augustmail.com>
Subject: Re: What does +FOO mean?
Message-Id: <slrndc4c27.8ej.tadmc@magna.augustmail.com>
John Bokma <john@castleamber.com> wrote:
> fishfry <BLOCKSPAMfishfry@your-mailbox.com> wrote:
>
>> I'm looking at a lot of code where they have
>>
>> use constant FOO => "foo";
>>
>> and then later
>>
>> my $hash{+FOO} ...
>>
>> Can someone please explain what '+' signifies in this context?
>
> $hash{FOO} is $hash{'FOO'}
> $hash{+FOO} is $hash{"foo"}
$hash{ FOO() } is $hash{"foo"} too.
(but the OP's "my $hash{+FOO}" isn't even Perl...)
The perl parser intuit()s that the FOO is a string, if you want it
to be a subroutine call instead (which is how "use constant"
implements constants), then you need to disambiguate it somehow
so that you get your desired semantic.
--
Tad McClellan SGML consulting
tadmc@augustmail.com Perl programming
Fort Worth, Texas
------------------------------
Date: 6 Apr 2001 21:33:47 GMT (Last modified)
From: Perl-Users-Request@ruby.oce.orst.edu (Perl-Users-Digest Admin)
Subject: Digest Administrivia (Last modified: 6 Apr 01)
Message-Id: <null>
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End of Perl-Users Digest V10 Issue 8212
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