Cleancode

Clean Code Hendrik Van Belleghem Belgian Perl Workshop 2007

It’s all Bruces fault!

Obviously? Pragmas

warnings

strict

subs : no barewords!

refs : no symbolic references!

vars : no undeclared variables!

Obviously? Variable names

Variable names should be

Short

but not too short

$i, $a, $o

Unambiguous

$i, $data, $line

Variable names should definitely not be generated by Acme::MetaSyntactic:

$thwacke # batman

$flrbbbbb # batman

$bondelschwaartz #pynchon

$ununquadium # elements

Acme::Metasyntactic? It’s all BooK’s fault!

Scalars are single

$item

Hashes and arrays are plural

@items

Mark booleans with test

$found_match

Add reference prefix/suffix

$item_ref

Braces.. bad?

Array definition

my @list =

( ‘larry’,

‘ damian’ );

Any other block?

for my $coder ( @list )

{ print “hi $coder ”; }

Braces..good?

Array definition

my @list = (

‘ larry’,

‘ damian’

);

Any other block?

for my $coder ( @list ) {

print “hi $coder ”;

}

Stay away from $_

$_ as default argument?

-X, abs, alarm, chomp, chop, chr, chroot, cos, defined, eval, exp, glob, hex, int, lc, lcfirst, length, log, lstat, oct , ord, pos, print, quotemeta, readlink, ref, require, reverse, rmdir, sin, split, sqrt, stat, study, uc, ucfirst, unlink

Implicit use

m//, s///, y///

for(), map {}, grep {}, while(<>)

default input and pattern matching space

Postfix if

buy("secret lair") and

buy("sharks with lasers")

and $mini_me = clone()

if $goal eq "world domination";

if ($goal eq “world domination”)

{ buy(“secret lair”);

buy(“sharks with lasers”);

$mini_me = clone();

}

C style loops

for (my $slide = 1; $slide < 25 ; $slide++)

{ present($slide); }

for my $slide (1..25)

{ present($slide); }

Cleaner

Easier to read

POD

Put POD in the source file..

At the end

Check your POD!

Podchecker

Use POD templates & stubs

NAME, VERSION, SYNOPSIS,..

String eval is bad

Don’t overuse eval.. Period

String eval is recompiled on execution

Use block instead

Are you taint-checking??

Filehandles

Bareword filehandles

Cannot be localized

Passing it to a sub?

Try typeglobs

Better: indirect filehandles

From 5.6 onwards

open my $filehandle, ”<filename” or die $!;

Regexp::Common

IP addresses?

$ip =~ /$RE{net}{IPv4}/

MAC addresses?

$ip =~ /$RE{net}{MAC}/

Credit cards

$number =~ /$RE{zip}{VISA}/

For all your extraordinary regexp needs

Regexp::Common?

It’s all Abigails fault!

Dutch

Tall

Strapping hunk of

manhood

For all your extraordinary regexp needs

Regexp Delimiters

Question..

What does this do?

harry s truman was the 33rd u.s. president;

harry s |ruman was |he 33rd u.s. presiden|;

harry($string =~ s{ruman was }{he 33rd u.s. presiden}xms);

Regexp

Keep it simple!

$foo =~ s{foo}{bar}g;

$html =~ s/<(?:[^>'"]*|(['"]).*?1)*>//gsx

Add comments to big Regexp chunks

Use A and instead of $ and ^

s{ < # opening angle bracket (?: # Non-backreffing grouping paren [^>'"] * # 0 or more things that are neither > nor ' nor " | # or else ".*?" # a section between double quotes (stingy match) | # or else '.*?' # a section between single quotes (stingy match) ) + # all occurring one or more times > # closing angle bracket }{}gsx; # replace with nothing, i.e. delete

Autoload

Inheritence precedence?

Catch all method

Refactoring

Original code

Duplicated code

Move to subroutines

Duplicated subroutines

Move to packages

No overkill!

Tests

Write tests first

Test::Simple & Test::More

Test for failures

Test the obvious & not so obvious

Find a bug? Write a test!

Version control

Multiple developers

Undo

Generate patches

Merging/branching

CVS, Subversion, RCS, Perforce, BitKeeper, git

Format

Compile time definition

No runtime changes

Except with eval

Global variables only

Output to named filehandle

Tie

Unknown magic

Unpredictable behavior

Eg: Tie::Scalar::RestrictUpdates limits changes

Slow

Change variable behavior through code

Perl::Critic

As Module

As command line tool

As website : http://perlcritic.com

DIY

Configurable

Perl::Critic

As Module

use Perl::Critic;

my $file = shift;

my $critic = Perl::Critic->new();

my @violations = $critic->critique($file);

print @violations;

Perl::Critic

lenore:~$ perlcritic -stern strict.pm Code before strictures are enabled at line 3, column 1. See page 429 of PBP. (Severity: 5) Code before warnings are enabled at line 3, column 1. See page 431 of PBP. (Severity: 4) Always unpack @_ first at line 11, column 1. See page 178 of PBP. (Severity: 4) Subroutine does not end with "return" at line 11, column 1. See page 197 of PBP. (Severity: 4) Always unpack @_ first at line 27, column 1. See page 178 of PBP. (Severity: 4) Subroutine does not end with "return" at line 27, column 1. See page 197 of PBP. (Severity: 4) Always unpack @_ first at line 32, column 1. See page 178 of PBP. (Severity: 4) Subroutine does not end with "return" at line 32, column 1. See page 197 of PBP. (Severity: 4)

Perl::Critic