In Perl 5, constants _are_ subroutines: 

use constant FOO => 42;

[download]
is basically syntactic sugar for: 
sub FOO { 42 }

[download]

Normally, you wouldn't need to use the & sigil, but many of the POSIX constants are basically AUTOLOADed subroutines. So I bet you have something like: 

use POSIX ();

[download]
at the start of your program. Because the subroutines have not been encountered at compile time, the compiler needs a hint that it is a subroutine (otherwise it will assume it is a "bareword"). Observe: 
$ perl -mPOSIX -e '$a = POSIX::O_RDWR; print "$a\n"'
POSIX::O_RDWR
$ perl -mPOSIX -e '$a = &POSIX::O_RDWR; print "$a\n"'
2

[download]

An alternate way is to export the constant your own namespace so that you can refer to it directly without the POSIX:: prefix: 

use POSIX qw(O_RDWR);

[download]
or, as a one liner: 
$ perl -mPOSIX=O_RDWR -e '$a = O_RDWR; print "$a\n"'
2

[download]

Hope this helps.

Liz

In reply to Re: Ampersand prefix for package constants ? by liz
in thread Ampersand prefix for package constants ? by Anonymous Monk

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.