From the source (op.c): 
case OP_CONST:
  sv = cSVOPo_sv;
  if (cSVOPo->op_private & OPpCONST_STRICT)
    no_bareword_allowed(o);
  else {
    if (ckWARN(WARN_VOID)) {
      useless = "a constant";
      /* don't warn on optimised away booleans, eg
       * use constant Foo, 5; Foo || print; */
      if (cSVOPo->op_private & OPpCONST_SHORTCIRCUIT)
        useless = 0;
      /* the constants 0 and 1 are permitted as they are
         conventionally used as dummies in constructs like
           1 while some_condition_with_side_effects;  */
      else if (SvNIOK(sv) &&
        (SvNV(sv) == 0.0 || SvNV(sv) == 1.0))
        useless = 0;

[download]
Basically, if you use 0 and or 1 and, etc., Perl won't warn about the useless use of a constant.
_____________________________________________________
Jeff[japhy]Pinyan: Perl, regex, and perl hacker, who'd like a job (NYC-area)
s++=END;++y(;-P)}y js++=;shajsj<++y(p-q)}?print:??;

In reply to Re: Warning messages about useless constants ignore '0's and '1's by japhy
in thread Warning messages about useless constants ignore '0's and '1's by Sandy

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.