Re: Warning messages about useless constants ignore '0's and '1's

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;
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Basically, if you use 0 and or 1 and, etc., Perl won't warn about the useless use of a constant.

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Re: Re: Warning messages about useless constants ignore '0's and '1's by ysth (Canon) on May 11, 2004 at 03:53 UTC
It will never warn about 0 or 1 in void context (including in a "list" specified in scalar context), and also will not warn about any constant on the left side of a short-circuiting op. You seem to have conflated the two cases.	[reply]