After more research I found a function that I was looking for 
 
sub is_const
{use B;B::SVf_READONLY & B::svref_2object(\$_[0])->FLAGS}

       my $m="va"; our $n=3; my $u=undef; our $u2=undef;
       for $x ($m, $n, $u, $u2, 4, "a", undef) 
       { print "$x ";$x="VAR" unless is_const($x); print $x,"\n\n" }

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but it too doesn't catch undef being passed it. For what I'm doing now, I don't think I'll encounter this condition. I think that japhy's is_const is 'better' than the flags code that I came across - at least it's easier to read.

What do you think?

In reply to Re: Re: Detecting constant arguments passed to subroutines by dcd
in thread Detecting constant arguments passed to subroutines by dcd

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