2017 twenty four merry days of Perl Feed

North Pole Safety Precautions

Import::Into - 2017-12-06

The Wise Old Elf was pair programming with Noel Cuddlecrackers, one of the newer elves to join Santa's merry little band of programmers.

Noel and he had agreed to start work on a really simple script. Noel opened a new file, and the Wise Old Elf watched patiently as Noel typed:


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use strict;
use warnings;

 

"Pretty good", the Wise Old Elf thought to himself, "at least he's enabling strictures to help catch mistakes". Noel kept typing though...


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no indirect;
 

"Excellent, Noel's not allowing calls of the form new Foo" the elder Elf thought to himself. But Noel wasn't done typing...


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no multidimensional;
 

"Okay, so Noel's disabling Perl's problematic multi-dimensional array syntax that no-one uses since we use arrays containing references to arrays these days" the Wise old Elf considered. But Noel still was typing more things...


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use autodie qw(:all);
 

"Now he's avoiding to have to manually check each time if one of Perl's IO routines succeeded, and just have them automatically throw an exception". Noel was still typing...


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use utf8;
 

"So he's allowing utf-8 encoding in the document so he can type non-ascii characters directly into the source" the Wise Old Elf mused.

Noel was still typing. The Wise Old Elf had to stop him before he became the Wise Much Older Elf.

"Noel", he asked, "exactly how much more boilerplate stuff are you going to type before we get to work?"

"Not much", the young faced worker replied, with a big grin on his face, "I just have to enable a few experimental features, monkey around with the method resolution order, and..."

"STOP", the Wise Old Elf firmly interrupted. "You do realize that we have a standard module that we use for our in house stuff that does all of this for us, don't you?" Indeed, it was true. A few years back the Wise Old Elf had monkeyed around with a Perl module called Import::Into that allowed a module to import modules into whoever used that module. This allowed the Wise Old Elf to create a standard boilerplate module that they now imported at the start of every Perl source file. Near the top of each file there simply was the line


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use NorthPole::Ourperl;
 

And all the source code that Cuddlecrackers wrote (and was going to add) could be replaced. Import::Into is simple to use - you simply call the fully qualified method import::into on the package name you want to import into whoever uses your module inside the import method:


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package NorthPole::Ourperl;
...

sub import {
# turn on 'use strict' in whoever does 'use NorthPole::Ourperl'
strict->import::into(1);
    ...
}

 

The full package that the North Pole is currently using looks like this:


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## no critic (NamingConventions::Capitalization)
package NorthPole::Ourperl;
## use critic (NamingConventions::Capitalization)

use strict;
use warnings;

our $VERSION = '1.000000';

use Import::Into;

# XXX - it'd be nice to include bareword::filehandles but this conflicts with
# autodie - see https://rt.cpan.org/Ticket/Display.html?id=93591
use autodie 2.25 ();
use IPC::System::Simple; # to fatalize system
use experimental ();
use feature ();
use indirect ();
use mro ();
use multidimensional ();

# This adds the UTF-8 layer on STDIN, STDOUT, STDERR for _everyone_
use open qw( :encoding(UTF-8) :std );
use utf8 ();

sub import {
    my $caller_level = 1;

    strict->import::into($caller_level);
    warnings->import::into($caller_level);

    my @experiments = qw(
        lexical_subs
        postderef
        signatures
    )
;
    experimental->import::into( $caller_level, @experiments );

    my ($version) = $^V =~ /^v(5\.\d+)/;
    feature->import::into( $caller_level, ':' . $version );
## no critic (Subroutines::ProhibitCallsToUnexportedSubs)
mro::set_mro( scalar caller(), 'c3' );
## use critic
utf8->import::into($caller_level);

    indirect->unimport::out_of( $caller_level, ':fatal' );
    multidimensional->unimport::out_of($caller_level);
    'open'->import::into( $caller_level, ':encoding(UTF-8)' );
    autodie->import::into( $caller_level, ':all' );
}

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This:

  • Enables strict
  • Enables warnings
  • Turns on the experimental lexical subs feature
  • Turns on the experimental postfix derefencing feature
  • Turns on the experimental signature feature
  • Turns on whatever standard features this version of Perl supports (e.g. say, etc)
  • Sets the method resolution in the module to be c3
  • Disables indirect method calls
  • Disables old-style multidimensional array simulation
  • Configures the filehandles to be UTF-8 everwhere
  • Enables autodie for all system calls

In one line!

Above source code example adapted from App::GHPT::Wrapper::Ourperl, Copyright (c) 2017 by MaxMind, Inc, licensed under the The Artistic License 2.0.
Gravatar Image This article contributed by: Mark Fowler <mark@twoshortplanks.com>