for reasons lost to history, someone used "$self" (hey, it's unique, right?) as cheaper than generating a unique ID
Unfortunately it turns out that it isn't very cheap at all (speed wise). In fact it's just about the worse possible choice :-) On my perl 5.8.7 this basic benchmark:
#! /usr/bin/perl
use strict;
use warnings;
{ package Base;
use Devel::Size ();
sub make_n {
my ($class, $n) = @_;
my @objects;
push @objects, $class->new for 1..$n;
return \@objects;
}
sub hidden_stuff { return }
sub size_of_n {
my ($class, $n) = @_;
my $objects = $class->make_n( $n );
my $stuff = [ $objects, $class->hidden_stuff ];
return( Devel::Size::total_size( $stuff ), $objects );
}
sub do_something {
my $class = shift;
my $self = $class->new;
$self->set_a( $self->get_a + 1 ) for ( 1 .. 100 );
die unless $self->get_a == 101;
}
}
{ package BlessedHash;
use base qw( Base );
sub new {
bless { a => 1, b => 2, c => 3, d => 4 }, shift;
}
sub get_a { $_[0]->{a} };
sub set_a { $_[0]->{a} = $_[1] };
}
{ package RefaddrCached;
use Scalar::Util ();
use base qw( Base );
my (%a, %b, %c, %d);
sub new {
my $self = bless \my $_tmp, shift;
$$self = Scalar::Util::refaddr( $self );
$a{ $$self } = 1;
$b{ $$self } = 2;
$c{ $$self } = 3;
$d{ $$self } = 4;
return $self;
}
sub get_a { $a{ ${$_[0]} } };
sub set_a { $a{ ${$_[0]} } = $_[1] };
sub DESTROY {
my $self = shift;
delete $a{ $$self };
delete $b{ $$self };
delete $c{ $$self };
delete $d{ $$self };
}
sub hidden_stuff { return [ \%a, \%b, \%c, \%d ] }
}
{ package RefaddrCall;
use Scalar::Util qw( refaddr );
use base qw( Base );
my (%a, %b, %c, %d);
sub new {
my $self = bless \my $_tmp, shift;
$a{ refaddr $self } = 1;
$b{ refaddr $self } = 2;
$c{ refaddr $self } = 3;
$d{ refaddr $self } = 4;
return $self;
}
sub get_a { $a{ refaddr $_[0] } };
sub set_a { $a{ refaddr $_[0] } = $_[1] };
sub DESTROY {
my $self = shift;
delete $a{ refaddr $self };
delete $b{ refaddr $self };
delete $c{ refaddr $self };
delete $d{ refaddr $self };
}
sub hidden_stuff { return [ \%a, \%b, \%c, \%d ] }
}
{ package SelfAsIndex;
use Scalar::Util qw( refaddr );
use base qw( Base );
my (%a, %b, %c, %d);
sub new {
my $self = bless \my $_tmp, shift;
$a{ $self } = 1;
$b{ $self } = 2;
$c{ $self } = 3;
$d{ $self } = 4;
return $self;
}
sub get_a { $a{ $_[0] } };
sub set_a { $a{ $_[0] } = $_[1] };
sub DESTROY {
my $self = shift;
delete $a{ $self };
delete $b{ $self };
delete $c{ $self };
delete $d{ $self };
}
sub hidden_stuff { return [ \%a, \%b, \%c, \%d ] }
}
{ package NumSelfAsIndex;
use Scalar::Util qw( refaddr );
use base qw( Base );
my (%a, %b, %c, %d);
sub new {
my $self = bless \my $_tmp, shift;
$a{ 0+$self } = 1;
$b{ 0+$self } = 2;
$c{ 0+$self } = 3;
$d{ 0+$self } = 4;
return $self;
}
sub get_a { $a{ 0+$_[0] } };
sub set_a { $a{ 0+$_[0] } = $_[1] };
sub DESTROY {
my $self = shift;
delete $a{ 0+$self };
delete $b{ 0+$self };
delete $c{ 0+$self };
delete $d{ 0+$self };
}
sub hidden_stuff { return [ \%a, \%b, \%c, \%d ] }
}
{ package ClassStd;
use base qw( Base );
use Class::Std;
my %a : ATTR( :get<a> :set<a> );
my (%b, %c, %d) :ATTR;
sub BUILD {
my ($self, $id) = @_;
$a{ $id } = 1;
$b{ $id } = 2;
$c{ $id } = 3;
$d{ $id } = 4;
}
# just a guess - maybe more hidden behind the scenes
sub hidden_stuff { return [ \%a, \%b, \%c, \%d ] }
}
use Devel::Symdump;
my @classes = sort grep { eval { $_->isa( 'Base' ) } && $_ ne 'Base' }
+
Devel::Symdump->rnew->packages;
my $n = 10000;
my @objects;
foreach my $class (@classes) {
my ($size, $objects) = $class->size_of_n( $n );
# we keep the objects around just in case having heavily populated
# attribute hashes affects the performance of the inside-out objec
+ts
push @objects, $objects;
print "$class x $n\t= $size bytes\n";
};
print "\n";
use Benchmark qw /cmpthese/;
cmpthese( -1, { map {
my $class = $_;
$class => sub { $class->do_something }
} @classes});
Gives me:
BlessedHash x 10000 = 2265688 bytes
ClassStd x 10000 = 2222948 bytes
NumSelfAsIndex x 10000 = 2219534 bytes
RefaddrCached x 10000 = 2300888 bytes
RefaddrCall x 10000 = 2226816 bytes
SelfAsIndex x 10000 = 2436816 bytes
Rate SelfAsIndex ClassStd NumSelfAsIndex RefaddrCall
+RefaddrCached BlessedHash
SelfAsIndex 1000/s -- -9% -12% -44%
+ -57% -59%
ClassStd 1100/s 10% -- -3% -38%
+ -53% -55%
NumSelfAsIndex 1131/s 13% 3% -- -36%
+ -52% -54%
RefaddrCall 1778/s 78% 62% 57% --
+ -24% -27%
RefaddrCached 2349/s 135% 114% 108% 32%
+ -- -4%
BlessedHash 2443/s 144% 122% 116% 37%
+ 4% --
with a plain $self index coming in a lot worse than the faster alternatives.
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