Constants created by use constant are actually functions, or at least act like them.

The parens aren't needed in the code you gave, but they don't harm anything either. 

>perl -MO=Concise -e"use constant BUFFER => 20; if (BUFFER() != 20) {}
+"
3  <@> leave[1 ref] vKP/REFC ->(end)
1     <0> enter ->2
2     <;> nextstate(main 72 -e:1) v ->3
-     <0> ex-const v/4 ->3
-e syntax OK

>perl -MO=Concise -e"use constant BUFFER => 20; if (BUFFER != 20) {}"
3  <@> leave[1 ref] vKP/REFC ->(end)
1     <0> enter ->2
2     <;> nextstate(main 72 -e:1) v ->3
-     <0> ex-const v/4 ->3
-e syntax OK

[download]

They do help in other circumstances, though. If a bareword is expected, then the constant will be treated as a bareword instead of as a constant. EXPR => might be the only problem. 

>perl -le"use constant FOO => 'abc'; print %{{ FOO => 'def' }};"
FOOdef

>perl -le"use constant FOO => 'abc'; print %{{ FOO() => 'def' }};"
abcdef

[download]

Update: Interestingly, neither $hash{EXPR} and sub(*)->{EXPR} treat the constant as a bareword. EXPR => might be the only case where it's an issue.

In reply to Re: use constant with parentheses by ikegami
in thread use constant with parentheses by perlfan99

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.