in reply to Re: Detecting constant arguments passed to subroutines
in thread Detecting constant arguments passed to subroutines

The is_const code doesn't seem to detect undef as a constant, although Devel::Peek reports it as READONLY 
perl -w -le 'sub is_const { !eval { ($_[0]) = $_[0]; 1; } }
 print "undef is ",(is_const(undef)?"":"not")," a constant"'
undef is not a constant

perl -MDevel::Peek -le 'Dump(undef)'
SV = NULL(0x0) at 0x8120d38
  REFCNT = 2147483622
  FLAGS = (READONLY)

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Re: Re: Re: Detecting constant arguments passed to subroutines
by dcd (Scribe) on May 17, 2001 at 01:39 UTC
    I just noticed the REFCNT the Devel::Peek::Dump(undef) printed
    That can't be right, can it?
[reply]
      Perhaps it's that high so that it never "dies"? And the reason it doesn't say undef is constant (from my function) is because undef = $foo is illegal, but (undef) = $foo isn't. Fix: 
      sub is_const { defined($_[0]) and !eval { ($_[0]) = $_[0]; 1 } }

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      japhy -- Perl and Regex Hacker
[reply]
[d/l]
      undef is a very popular value! :)
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