Re: Re: Detecting constant arguments passed to subroutines

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" }
[download]

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?

Comment on Re: Re: Detecting constant arguments passed to subroutines Download Code

Replies are listed 'Best First'.
Re: Detecting constant arguments passed to subroutines by dcd (Scribe) on May 29, 2001 at 10:30 UTC
I just found the real functions I was looking for `readonly` in `Scalar::Util`. I haven't figured out yet why calling it indirectly via the is_const function doesn't detect that undef is a constant, as perl dies with an error when trying to modify the undef constant, but at least the `readonly` is easier to read and comprehend. If anyone can explain the undetect undef constant in is_const I'd be greatful. `use Scalar::Util 'readonly'; sub is_const { readonly($_[0]); } print "undef is readonly\n" if readonly(undef); print "undef not detected in is_const\n" unless is_const(undef); for $x (4, "a", undef) { print "$x ";$x="VAR" unless readonly($x); print $x,"\n"; } for $x (4, "a", undef) { print "$x ";$x="VAR" unless is_const($x); print $x,"\n"; }` [download]	[reply] [d/l] [select]
Re^2: Detecting constant arguments passed to subroutines by Anonymous Monk on Sep 14, 2005 at 00:24 UTC
It is a difference between: sub is_const { readonly($_[0]); } sub is_const { readonly(@_); } sub is_const { readonly($_); } -- Lubomir Host 'rajo' http://rajo.platon.sk	[reply]


Just another Perl shrine
	PerlMonks