comment on

I wanted to use Scalar::Util::readonly() to help distinguish between foo( 1,2,3) and foo( -one => 1, -two => 2, -three => 3), but it looks like there is an error (or at least an unexpected behaviour) in Perl. At least in my version. If I call foo( named => 1) then $_[0] is readonly, if I call foo( -named => 1), it's not.

use strict;
use Carp;
use Scalar::Util qw(readonly);

sub ro {
    print "readonly($_[0])=".readonly($_[0])."\n";
    $_[0] = 'xxx';
}
eval { ro('lonely') } or print $@;
eval { ro(named => 4); } or print $@;
eval { ro(-named => 7); } or print $@;

for (1..5) { # to test whether changing $_[0] affects the literal
  eval { ro(-loop => 7); } or print $@;
}
[download]

I guess the

V:\>perl -MO=Deparse -e "%a = (-foo => 1);"
(%a) = (-'foo', 1);
-e syntax OK
[download]

explains it ... I expected the -foo => 1 to be parsed as (or optimized to) '-foo' => 1, but it looks like its not. What do you get with your version of perl?

Update: There seems to be a speed difference as well:

use strict;
use Benchmark;

sub woH {
    my %a = (
        -a => 1, -a => 1, -a => 1, -a => 1, -a => 1, -a => 1, -a => 1,
+ -a => 1, -a => 1, -a => 1, -a => 1, -a => 1, -a => 1, -a => 1, -a =>
+ 1, -a => 1, -a => 1, -a => 1, -a => 1, -a => 1, -a => 1, -a => 1, -a
+ => 1,
        -a => 1, -a => 1, -a => 1, -a => 1, -a => 1, -a => 1, -a => 1,
+ -a => 1, -a => 1, -a => 1, -a => 1, -a => 1, -a => 1, -a => 1, -a =>
+ 1, -a => 1, -a => 1, -a => 1, -a => 1, -a => 1, -a => 1, -a => 1, -a
+ => 1,
        -a => 1, -a => 1, -a => 1, -a => 1, -a => 1, -a => 1, -a => 1,
+ -a => 1, -a => 1, -a => 1, -a => 1, -a => 1, -a => 1, -a => 1, -a =>
+ 1, -a => 1, -a => 1, -a => 1, -a => 1, -a => 1, -a => 1, -a => 1, -a
+ => 1,
        -a => 1, -a => 1, -a => 1, -a => 1, -a => 1, -a => 1, -a => 1,
+ -a => 1, -a => 1, -a => 1, -a => 1, -a => 1, -a => 1, -a => 1, -a =>
+ 1, -a => 1, -a => 1, -a => 1, -a => 1, -a => 1, -a => 1, -a => 1, -a
+ => 1,
        -a => 1, -a => 1, -a => 1, -a => 1, -a => 1, -a => 1, -a => 1,
+ -a => 1, -a => 1, -a => 1, -a => 1, -a => 1, -a => 1, -a => 1, -a =>
+ 1, -a => 1, -a => 1, -a => 1, -a => 1, -a => 1, -a => 1, -a => 1, -a
+ => 1,
    );
    return;
}

sub wH {
    my %a = (
        '-a' => 1, '-a' => 1, '-a' => 1, '-a' => 1, '-a' => 1, '-a' =>
+ 1, '-a' => 1, '-a' => 1, '-a' => 1, '-a' => 1, '-a' => 1, '-a' => 1,
+ '-a' => 1, '-a' => 1, '-a' => 1, '-a' => 1, '-a' => 1, '-a' => 1, '-
+a' => 1, '-a' => 1, '-a' => 1, '-a' => 1, '-a' => 1,
        '-a' => 1, '-a' => 1, '-a' => 1, '-a' => 1, '-a' => 1, '-a' =>
+ 1, '-a' => 1, '-a' => 1, '-a' => 1, '-a' => 1, '-a' => 1, '-a' => 1,
+ '-a' => 1, '-a' => 1, '-a' => 1, '-a' => 1, '-a' => 1, '-a' => 1, '-
+a' => 1, '-a' => 1, '-a' => 1, '-a' => 1, '-a' => 1,
        '-a' => 1, '-a' => 1, '-a' => 1, '-a' => 1, '-a' => 1, '-a' =>
+ 1, '-a' => 1, '-a' => 1, '-a' => 1, '-a' => 1, '-a' => 1, '-a' => 1,
+ '-a' => 1, '-a' => 1, '-a' => 1, '-a' => 1, '-a' => 1, '-a' => 1, '-
+a' => 1, '-a' => 1, '-a' => 1, '-a' => 1, '-a' => 1,
        '-a' => 1, '-a' => 1, '-a' => 1, '-a' => 1, '-a' => 1, '-a' =>
+ 1, '-a' => 1, '-a' => 1, '-a' => 1, '-a' => 1, '-a' => 1, '-a' => 1,
+ '-a' => 1, '-a' => 1, '-a' => 1, '-a' => 1, '-a' => 1, '-a' => 1, '-
+a' => 1, '-a' => 1, '-a' => 1, '-a' => 1, '-a' => 1,
        '-a' => 1, '-a' => 1, '-a' => 1, '-a' => 1, '-a' => 1, '-a' =>
+ 1, '-a' => 1, '-a' => 1, '-a' => 1, '-a' => 1, '-a' => 1, '-a' => 1,
+ '-a' => 1, '-a' => 1, '-a' => 1, '-a' => 1, '-a' => 1, '-a' => 1, '-
+a' => 1, '-a' => 1, '-a' => 1, '-a' => 1, '-a' => 1,
    );
    return;
}

timethese 100000, {
    woH => \&woH,
    wH => \&wH,
}
__END__
Benchmark: timing 100000 iterations of wH, woH...
        wH:  1 wallclock secs ( 1.45 usr +  0.00 sys =  1.45 CPU) @ 68
+917.99/s (n=100000)
       woH:  3 wallclock secs ( 2.39 usr +  0.00 sys =  2.39 CPU) @ 41
+893.59/s (n=100000)

Benchmark: timing 100000 iterations of wH, woH...
        wH:  2 wallclock secs ( 1.47 usr +  0.01 sys =  1.48 CPU) @ 67
+521.94/s (n=100000)
       woH:  2 wallclock secs ( 2.32 usr +  0.02 sys =  2.34 CPU) @ 42
+735.04/s (n=100000)

Benchmark: timing 100000 iterations of wH, woH...
        wH:  1 wallclock secs ( 1.42 usr +  0.00 sys =  1.42 CPU) @ 70
+472.16/s (n=100000)
       woH:  3 wallclock secs ( 2.56 usr +  0.00 sys =  2.56 CPU) @ 39
+077.76/s (n=100000)
[download]

Another strange thing:

D:\>perl -MO=Deparse -e "print -'ahoj' => 1"
print '-ahoj', 1;
-e syntax OK

D:\>perl -MO=Deparse -e "print -ahoj => 1"
print -'ahoj', 1;
-e syntax OK
[download]

Jenda
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Defend the free world!

In reply to -foo not readonly in fun(-foo => 1) in perl v5.8.7 by Jenda

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