Perl 5.12 for Everyday Use

Perl 5.12
for everyday use

Sunday, December 5, 2010

5.12 isn’t like 5.10

perl5100delta


- after 5.8, we had to wait 5 years for 5.10

perl5100delta


- after 5.8, we had to wait 5 years for 5.10
- 5.12 came out 2 years after 5.10

perl5100delta

5.12 is a Nice Change

perl5100delta


- 5.10 was a huge set of changes

perl5100delta


- 5.12 is a lot smaller

perl5100delta


- 5.12 is not as compelling as 5.10

perl5100delta


- 5.12 is not as compelling as 5.10
- and that’s a good thing

perl5100delta

5.12 is a Mixed Bag

perl5100delta

5.12 is a Mixed Bag

- this talk isn’t just for beginners

perl5100delta

5.12 is a Mixed Bag

- some of these changes are at the edges

perl5100delta

5.12 is a Mixed Bag

- but they’re all practical

perl5100delta

5.12 is a Mixed Bag

- but they’re all practical
- except for the ones that aren’t

perl5100delta

By the way, 5.14...

perl5132delta

By the way, 5.14...

- is going to be awesome

perl5132delta

By the way, 5.14...

- and available in about nine months

perl5132delta

By the way, 5.14...

- and available in about nine months
- and it’s going to be awesome

perl5132delta

...and 5.10 is frozen.

perl5101delta


- 5.10 is the last release of the old way

perl5101delta


- that means it got some features backported

perl5101delta


- that will never happen again

perl5101delta


- that will never happen again
- I’ll point out 5.12isms that got into 5.10.1

perl5101delta

but enough about other versions


let’s talk about 5.12


First: A Warning

feature

First: A Warning
- 5.12 is backwards compatible

feature

First: A Warning
- but adds new keywords and operators

feature

First: A Warning
- they’re not enabled by default

feature

First: A Warning
- use feature ‘mtfnpy’;

feature

First: A Warning

- use 5.012;

feature

First: A Warning

- use 5.012;

- read the perldoc
feature

First: A Warning

- use 5.012;

- read the perldoc I’m a perldoc
ref!
feature

$old ~~ $new

- the smart match operator changed

also in 5.10.1
perlsyn

~~

- no longer commutative; right side wins
- non-overloaded objects can’t be ~~ed
- still very complicated (23 behaviors)
- you won’t be using this every day

perldoc

autodie

also in 5.10.1
autodie

autodie

- like Fatal

also in 5.10.1
autodie

autodie

- like Fatal
- but deadlier

also in 5.10.1
autodie

autodie

open my $fh, ‘>‘, $filename;

while (<$fh>) {
...
}

close $fh;

autodie

autodie
open my $fh, ‘>‘, $filename
or die “couldn’t open $filename: $!”;

while (<$fh>) {
...
}

close $fh
or die “couldn’t close $filename: $!”;

autodie

autodie
use autodie;

open my $fh, ‘<‘, $filename;

while (<$fh>) {
...
}

close $fh;

autodie

autodie
use autodie;

open my $fh, ‘>‘, $filename;

while (<$fh>) {
no autodie;
rmdir or warn “couldn’t remove $_: $!”;
}

close $fh;

autodie

autodie problems

- autodie doesn’t affect print
- you must close filehandles explicitly

perldoc

Unicode


Perl is Good at Unicode

perlunicode

Perl 5.12 is Better

perlunicode

Perl 5.12 is Better

- Unicode 5.2

perlunicode

Perl 5.12 is Better

- Unicode 5.2
- every character property is available

perlunicode

Perl 5.12 is Better

- Unicode 5.2
- every character property is available
- X in regex is more sensible

perlunicode

“The Unicode Bug”

perlunicode


- strings aren’t always treated as Unicode

perlunicode


- this causes weird bugs that take ages to find

perlunicode


- this causes weird bugs that take ages to find
- use feature ‘unicode_strings’;

perlunicode

use feature ‘unicode_strings’;

perldoc

use 5.12.0;

perldoc

use 5.10.0;

perldoc

use 5.10.0;

use feature qw(
say
state
switch
);

perldoc

use 5.12.0;

use feature qw(
say
state
switch
unicode_strings
);

perldoc

use 5.12.0;

use feature qw(
say
state
switch
unicode_strings
);

use strict;

perldoc

Container Improvements


my %hash = (a => 1, b => 2);

while (my ($k, $v) = each %hash) {
say “value for $k is $v”;
}


my %hash = (a => 1, b => 2);

}

value for a is 1
value for b is 2


my @array = qw(a b);



value for 0 is b
value for 1 is a



for my $k (0 .. $#array) {
say “value for $k is $array[$k]”;
}

value for 0 is b
value for 1 is a



while (my ($k, $v) = each @array) {
}

value for 0 is b
value for 1 is a



for my $k (0 .. $#array) {
say “value for $k is $array[$k]”;
}


}


sub redump {
my ($href) = @_;
}
}

my %hash = (a => 1, b => 2);

print “== $k ==”;
redump(%hash);
}



}




do_something(@array);
}



my $string = $part_for_maybe_transient->bodyhandle->as_string;
my $transient_pos = _match_position($string, $Not_An_Error);
last unless defined $transient_pos;
my $permanent_pos = _match_position($string, $Really_An_Error);
my $orig_msg_pos = _match_position($string, $Returned_Message_Below);
last if _position_before($permanent_pos, $orig_msg_pos);
if (_position_before($transient_pos, $orig_msg_pos)) {
last if $message->effective_type eq ‘multipart/report’;
last if !$first_part
|| $first_part->effective_type ne ‘text/plain’;
my $string = $first_part->as_string;
last if length($string) > 3000;
# added return receipt (fix for bug #41870)
last if $string !~ /auto.{0,20}reply|return receipt
|vacation|(out|away|on holiday).*office/i;
$self->log(“looks like an autoreply, ignoring.”);
$self->{type} = “vacation autoreply”;
$self->{is_bounce} = 0;
return $self;
}
}


AVOID
each @array


local ??


use Ancient::Utility qw(stuff);

my $result = do {
local $Ancient::Utility::WIDTH = 10;
stuff( $input );
};


my $href = { a => 1, b => 2 };

my $result = do {
local $href->{a} = 3;
stuff( $href );
};


my $href = { a => 1, b => 2 };

my $result = do {
delete local $href->{a};
stuff( $href );
};


$]


$[


$[ - first index of array

perlvar


- so you can make $array[1] mean first

perlvar


- isn’t that awesome???

perlvar


- isn’t that awesome???
- yeah, about as awesome as Comic Sans

perlvar

$[

$[ = 1;

for (1 .. $#array) {
...
}

perlvar

$[

for ($[ .. $#array) {
...
}

perlvar

$[

Assigned to $[. Are you some kind of
idiot or something? at -e line 123.

perlvar

$[

Use of assignment to $[ is deprecated
at -e line 123.

perlvar

More About Deprecations


@INC


@INC:
/usr/pkg/lib/perl5/5.8.0/i386-solaris
/usr/pkg/lib/perl5/5.8.0
/usr/pkg/lib/perl5/site_perl/5.8.0/i386-solaris
/usr/pkg/lib/perl5/site_perl/5.8.0
/usr/pkg/lib/perl5/site_perl
/usr/pkg/lib/perl5/vendor_perl/5.8.0/i386-solaris
/usr/pkg/lib/perl5/vendor_perl/5.8.0
/usr/pkg/lib/perl5/vendor_perl

perlvar

@INC:
/usr/pkg/lib/perl5/site_perl/5.8.0/i386-solaris
/usr/pkg/lib/perl5/site_perl/5.8.0
/usr/pkg/lib/perl5/site_perl
/usr/pkg/lib/perl5/vendor_perl/5.8.0/i386-solaris
/usr/pkg/lib/perl5/vendor_perl/5.8.0
/usr/pkg/lib/perl5/vendor_perl
/usr/pkg/lib/perl5/5.8.0/i386-solaris
/usr/pkg/lib/perl5/5.8.0

perlvar

now we can remove stuff
from the core distribution


Class::ISA
Pod::Plainer
Shell


Class::ISA
Pod::Plainer
Shell
Switch


… and …


my $x = get_input;


my $x = get_input;

if ( $x >= 0 ) {


my $x = get_input;

if ( $x >= 0 ) {
do_something for 0 .. $x;


my $x = get_input;

if ( $x >= 0 ) {
} else {


my $x = get_input;

if ( $x >= 0 ) {
} else {
...


my $x = get_input;

if ( $x >= 0 ) {
} else {
...
}


my $x = get_input;

if ( $x >= 0 ) {
} else {
die “Unimplemented”
}


sub virtual_method { ... }


sub method_I_will_write_later { ... }


Unimplemented at Some::Library line 123


AVOID
...


AVOID
...
(except maybe in slides and pseudocode)


sub virtual_method {
confess ‘...’
}

sub method_I_will_write_later {
confess ‘...’
}


error message
improvements


perldiag

perl -MCGI -e’my $q = CGI->new;’
Unrecognized character xE2 in column
12 at -e line 1.

perldiag

perl -MCGI -e’my $q = CGI->new;’
Unrecognized character xE2 in column
12 at -e line 1.

perl -MCGI -e’my $q = CGI−->new;’
Unrecognized character xE2; marked
by <-- HERE after y $q = CGI<-- HERE
near column 12 at -e line 1.

perldiag

My Favorite 5.10-ism?

$str = “Greetings, $name. Your last
login was $last. It is now $time.”;

Use of uninitialized value $time in
concatenation (.) or string at
hello.plx line 9.

perldiag

if (length $input->{new_email}) {
$user->update_email(...);
}

perldiag

if (length $input->{new_email}) {
$user->update_email(...);
}

Use of uninitialized value in length
at - line 3120.

perldiag

overloading


my $object = Object->new;

print $object;


my $object = Object->new;

{
no overloading;
print $object;
}


my $filename = get_filename;

if (-d $filename) {
handle_directory($filename);
}


package Filename;

use overload ‘-X’ => sub {
my ($self, $test) = @_;
return $self->is_dir if $test eq ‘d’;
return $self->cd_able if $test eq ‘x’;
...;
};


my $file = get_file;

if (-d $file) {
handle_directory($file);
}


my $filename = get_file;

if (-d $file and -x _) {
handle_directory($file);
}


my $filename = get_filename;

if (-d -x $filename) {
handle_directory($filename);
}


AVOID
overload -X


y2038


~$ perl5.10.0 -E ‘say scalar localtime 2**31-1’


Mon Jan 18 22:14:07 2038


Mon Jan 18 22:14:07 2038

~$ perl5.10.0 -E ‘say scalar localtime 2**31’


Mon Jan 18 22:14:07 2038

Fri Dec 13 15:45:52 1901


Mon Jan 18 22:14:07 2038


Mon Jan 18 22:14:07 2038

Mon Jan 18 22:14:08 2038


some non-everyday changes


Method Resolution Order
A

B C

D

mro

A

- 5.8 : D, B, A, C
B C

D

mro

A

- 5.8 : D, B, A, C
- 5.10: D, B, C, A B C

D

mro

A

- 5.8 : D, B, A, C
- 5.10: D, B, C, A B C

- 5.12: Anything!
D

mro

A

- 5.8 : D, B, A, C
- 5.10: D, B, C, A B C

- 5.12: F
D

MRO::Define

use strict;
use warnings;

package Booster::Gold;
our $VERSION = ‘1.00’;

...

1;


use 5.12.0;
use warnings;

package Booster::Gold 1.00;

...

1;


use 5.14.0;
use warnings;

package Booster::Gold 1.00 {
...
}

1;


http://www.perl.org/get.html


Any questions?


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