XAS::Docs::StyleGuide - How to write new code
All programmers develop a style for their code. It has been suggested that this style can even be used to determine who contributed what, for any given project. Interesting if true.
Code should be easy to read and have a nice flow, some would say it should be elegant. Any programmer should be able to sit down and figure out what it does in a relatively short time. This means all those nice Perl tricks should be kept to a minimum. Remember you may not be the only person that needs to read and understand your code.
The style that I prefer has been developed over the past 25 years. It has been successfully used with different languages and environments. I first started using it with BASICPLUS 2 on the PDP 11/70 running RSTS/E. Yeah, I have been around that long.
White space is your friend. It is there to help you read the code. Compilers and interpreters don't care about white space, you should. I find the following code hard to read.
if($something==$this){ do_this(); }
A more condensed version would be like this.
if($something==$this){do_this();}
or
do_this()if($something==$this);
or that BASICPLUS 2
10 if something = this then \ call do_this \ end if
or the more condensed version
10 if something = this then:call do_this:end if
or the really condensed version
10 call do_this if something = this
Perfectly valid code for the compiler, but extremely hard for the programmer to read. I find this much easier to read.
if ($something == $this) { do_this(); }
Which leads into the next topic.
There are many ways to do bracing. Most of it originated in the C world and migrated to other environments. I prefer the bracing on the same line as the statement with the trailing brace in the starting column of that block. Here are some examples.
while ($this != $done) { }
do { } while ($this == $running);
foreach my $a (@array) { }
if ($something == $that) { } elsif { } else { }
or even this
{ # some additional code here }
Notice how I like to but parens around the conditional for the if statements. To me, it is easier to read.
Indenting code makes for readable code. This is a good thing. Just ask the Python guys. Indents should be 4 spaces. I know that some people think this should be handled as tabs. With the terminals tab spacing set to whatever, so the code lines up nicely. That may have been true when the Teletype 33 was dying and the vt100 was king. But with modern terminal emulators, fancy IDE editors, and web based pretty printers, the tab spacing just never matches up. Especially when two people are using both styles in the same file.
With the usage of white space and indention, you can have fairly readable code. For example a subroutine would be written like this.
sub routine { my $p1 = shift; my $p2 = shift; if ($p1 == $p2) { do_something(); } }
Which is straight forward and easy on the eyes.
As everyone knows, god created the 80 by 24 character terminal and you shall use it. I don't care if you have a 32" monitor and want to run your IDE in full screen mode. Line wrap will happen at character 75, unless the line makes sense going farther.
Variable names should make sense. A one character variable name makes sense when used as an incremental. They should be lowercase and use "_" to denote meaning. No CamelCase or Hungarian Notation here. Variables should be declared at the beginning of the routine unless there scope needs to be limited. For example.
sub routine { my $p1 = shift; for (my $x = 0; $x < $p1; $x++) { do_something($x); } }
There is no need to declare $x for the entire routine, as it is the increment for the loop.
Remember that 80 by 24 terminal. Size matters. Your subroutine should fit within a terminal screen. If bigger, consider breaking it up.
Function, method, subroutine or whatever you call them, should be lowercase and use "_" to denote meaning. Once again, no CamelCase here.
A leading "_" indicates a private method. Due to the nature of Perl. It is not easy to truly have private methods. If somebody abuses your code and uses your private methods, including me. It is their problem, should they get bitten by code changes.
If you really thing you need them, may I suggest C#. It is a nice little bondage language, that will let you do all that Computer Science stuff, that your professors thought were important. Hey, it would might even run on Linux...
If you pass parameters to your subroutines, they should be validated if they are a public interface. A validation method is supplied and uses Params::Validate as the validation engine. If more the two parameters are passed they need to be named and the parameter name must start with a "-". For example:
package Package; our $VERSION = '0.01'; use XAS::Class debug => 0, version => $VERSION, base => 'XAS::Base', utils => ':validation', ; sub routine { my $self = shift; my ($p1, $p2) = validate_params(\@_, [1,1]); }
or with named parameters
sub routine { my $self = shift; my $p = validate_params(\@_, { -p1 => 1, -p2 => 1, }); my $p1 = $p->{'p1'}; my $p2 = $p->{'p2'}; }
or as a plain package routine
package Package; our $VERSION = '0.01'; use XAS::Utils ':validation'; sub routine { my $p = validate_params(\@_, { -p1 => 1, -p2 => 1, }); my $p1 = $p->{'p1'}; my $p2 = $p->{'p2'}; }
For the most part error handling is done thru exceptions and those exceptions have names and those names have meaning. Those names should be lower case and have dot (.) separators. The utility function dotid() is very handy when creating those names. Example:
package Package; our $VERSION = '0.01'; use Try::Tiny; use XAS::Class debug => 0, version => $VERSION, base => 'XAS::Base', mixin => 'XAS::Lib::Mixins::Handler', utils => ':validation dotid', ; sub routine { my $self = shift; my ($p1, $p2) = validate_params(\@_, [1,1]); try { If ($p1 == $p2) { do_something(); } else { $self->throw_msg( dotid($self->class) . '.routine.notequal', 'notequal', $p1, $p2 ); } } catch { my $ex = $_; $self->exception_handler($ex); }; } 1;
The name of this exception would be 'package.routine.notequal' were 'notequal' would be the exception type. The message for this exception is 'notequal' and would have the format of "%s is not equal to %s". This is a quick and easy way to find problems in your code.
I don't believe in excessive comments. They clutter the code and are usually wrong. Comments should only be used when something out of the ordinary is about to happen. Otherwise the actual code should be sufficient. It's all that white space and indenting, it really works.
Documentation is good. It should be at the end of the file after the code. I find POD intertwined with the code to be hard to read. And please run the documentation thru a spell checker.
There are several templates provided to help write code. Use them, they are boiler plate, where you just fill in the blanks and start coding.
Kevin L. Esteb, <kevin@kesteb.us>
Copyright (c) 2012-2015 Kevin L. Esteb
This is free software; you can redistribute it and/or modify it under the terms of the Artistic License 2.0. For details, see the full text of the license at http://www.perlfoundation.org/artistic_license_2_0.
To install XAS, copy and paste the appropriate command in to your terminal.
cpanm
cpanm XAS
CPAN shell
perl -MCPAN -e shell install XAS
For more information on module installation, please visit the detailed CPAN module installation guide.