path: root/user_guide_src/source/general/styleguide.rst

###############
PHP Style Guide
###############


The following page describes the use of coding rules adhered to when
developing CodeIgniter.

.. contents:: Table of Contents

File Format
===========

Files should be saved with Unicode (UTF-8) encoding. The BOM should
*not* be used. Unlike UTF-16 and UTF-32, there's no byte order to
indicate in a UTF-8 encoded file, and the BOM can have a negative side
effect in PHP of sending output, preventing the application from being
able to set its own headers. Unix line endings should be used (LF).

Here is how to apply these settings in some of the more common text
editors. Instructions for your text editor may vary; check your text
editor's documentation.

TextMate
''''''''

#. Open the Application Preferences
#. Click Advanced, and then the "Saving" tab
#. In "File Encoding", select "UTF-8 (recommended)"
#. In "Line Endings", select "LF (recommended)"
#. *Optional:* Check "Use for existing files as well" if you wish to
   modify the line endings of files you open to your new preference.

BBEdit
''''''

#. Open the Application Preferences
#. Select "Text Encodings" on the left.
#. In "Default text encoding for new documents", select "Unicode (UTF-8,
   no BOM)"
#. *Optional:* In "If file's encoding can't be guessed, use", select
   "Unicode (UTF-8, no BOM)"
#. Select "Text Files" on the left.
#. In "Default line breaks", select "Mac OS X and Unix (LF)"

PHP Closing Tag
===============

The PHP closing tag on a PHP document **?>** is optional to the PHP
parser. However, if used, any whitespace following the closing tag,
whether introduced by the developer, user, or an FTP application, can
cause unwanted output, PHP errors, or if the latter are suppressed,
blank pages. For this reason, all PHP files should **OMIT** the closing
PHP tag, and instead use a comment block to mark the end of file and
it's location relative to the application root. This allows you to still
identify a file as being complete and not truncated.

**INCORRECT**::

	<?php

	echo "Here's my code!";

	?>

**CORRECT**::

	<?php

	echo "Here's my code!";

	/* End of file myfile.php */
	/* Location: ./system/modules/mymodule/myfile.php */

Class and Method Naming
=======================

Class names should always start with an uppercase letter. Multiple words
should be separated with an underscore, and not CamelCased. All other
class methods should be entirely lowercased and named to clearly
indicate their function, preferably including a verb. Try to avoid
overly long and verbose names.

**INCORRECT**::

	class superclass
	class SuperClass

**CORRECT**::

	class Super_class

::

	class Super_class {

		public function __construct()
		{

		}
	}

Examples of improper and proper method naming:

**INCORRECT**::

	function fileproperties()		// not descriptive and needs underscore separator
	function fileProperties()		// not descriptive and uses CamelCase
	function getfileproperties()		// Better!  But still missing underscore separator
	function getFileProperties()		// uses CamelCase
	function get_the_file_properties_from_the_file()	// wordy

**CORRECT**::

	function get_file_properties()	// descriptive, underscore separator, and all lowercase letters

Variable Names
==============

The guidelines for variable naming is very similar to that used for
class methods. Namely, variables should contain only lowercase letters,
use underscore separators, and be reasonably named to indicate their
purpose and contents. Very short, non-word variables should only be used
as iterators in for() loops.

**INCORRECT**::

	$j = 'foo';		// single letter variables should only be used in for() loops
	$Str			// contains uppercase letters
	$bufferedText		// uses CamelCasing, and could be shortened without losing semantic meaning
	$groupid		// multiple words, needs underscore separator
	$name_of_last_city_used	// too long

**CORRECT**::

	for ($j = 0; $j < 10; $j++)
	$str
	$buffer
	$group_id
	$last_city

Commenting
==========

In general, code should be commented prolifically. It not only helps
describe the flow and intent of the code for less experienced
programmers, but can prove invaluable when returning to your own code
months down the line. There is not a required format for comments, but
the following are recommended.

`DocBlock <http://manual.phpdoc.org/HTMLSmartyConverter/HandS/phpDocumentor/tutorial_phpDocumentor.howto.pkg.html#basics.docblock>`_
style comments preceding class and method declarations so they can be
picked up by IDEs::

	/**
	 * Super Class
	 *
	 * @package	Package Name
	 * @subpackage	Subpackage
	 * @category	Category
	 * @author	Author Name
	 * @link	http://example.com
	 */
	class Super_class {

::

	/**
	 * Encodes string for use in XML
	 *
	 * @param	string
	 * @return	string
	 */
	function xml_encode($str)

Use single line comments within code, leaving a blank line between large
comment blocks and code.

::

	// break up the string by newlines
	$parts = explode("\n", $str);

	// A longer comment that needs to give greater detail on what is
	// occurring and why can use multiple single-line comments.  Try to
	// keep the width reasonable, around 70 characters is the easiest to
	// read.  Don't hesitate to link to permanent external resources
	// that may provide greater detail:
	//
	// http://example.com/information_about_something/in_particular/

	$parts = $this->foo($parts);

Constants
=========

Constants follow the same guidelines as do variables, except constants
should always be fully uppercase. *Always use CodeIgniter constants when
appropriate, i.e. SLASH, LD, RD, PATH_CACHE, etc.*

**INCORRECT**::

	myConstant	// missing underscore separator and not fully uppercase
	N		// no single-letter constants
	S_C_VER		// not descriptive
	$str = str_replace('{foo}', 'bar', $str);	// should use LD and RD constants

**CORRECT**::

	MY_CONSTANT
	NEWLINE
	SUPER_CLASS_VERSION
	$str = str_replace(LD.'foo'.RD, 'bar', $str);

TRUE, FALSE, and NULL
=====================

**TRUE**, **FALSE**, and **NULL** keywords should always be fully
uppercase.

**INCORRECT**::

	if ($foo == true)
	$bar = false;
	function foo($bar = null)

**CORRECT**::

	if ($foo == TRUE)
	$bar = FALSE;
	function foo($bar = NULL)

Logical Operators
=================

Use of **\|\|** is discouraged as its clarity on some output devices is
low (looking like the number 11 for instance). **&&** is preferred over
**AND** but either are acceptable, and a space should always precede and
follow **!**.

**INCORRECT**::

	if ($foo || $bar)
	if ($foo AND $bar)  // okay but not recommended for common syntax highlighting applications
	if (!$foo)
	if (! is_array($foo))

**CORRECT**::

	if ($foo OR $bar)
	if ($foo && $bar) // recommended
	if ( ! $foo)
	if ( ! is_array($foo))
	

Comparing Return Values and Typecasting
=======================================

Some PHP functions return FALSE on failure, but may also have a valid
return value of "" or 0, which would evaluate to FALSE in loose
comparisons. Be explicit by comparing the variable type when using these
return values in conditionals to ensure the return value is indeed what
you expect, and not a value that has an equivalent loose-type
evaluation.

Use the same stringency in returning and checking your own variables.
Use **===** and **!==** as necessary.

**INCORRECT**::

	// If 'foo' is at the beginning of the string, strpos will return a 0,
	// resulting in this conditional evaluating as TRUE
	if (strpos($str, 'foo') == FALSE)

**CORRECT**::

	if (strpos($str, 'foo') === FALSE)

**INCORRECT**::

	function build_string($str = "")
	{
		if ($str == "")	// uh-oh!  What if FALSE or the integer 0 is passed as an argument?
		{

		}
	}

**CORRECT**::

	function build_string($str = "")
	{
		if ($str === "")
		{

		}
	}


See also information regarding
`typecasting <http://us3.php.net/manual/en/language.types.type-juggling.php#language.types.typecasting>`_,
which can be quite useful. Typecasting has a slightly different effect
which may be desirable. When casting a variable as a string, for
instance, NULL and boolean FALSE variables become empty strings, 0 (and
other numbers) become strings of digits, and boolean TRUE becomes "1"::

	$str = (string) $str; // cast $str as a string

Debugging Code
==============

No debugging code can be left in place for submitted add-ons unless it
is commented out, i.e. no var_dump(), print_r(), die(), and exit()
calls that were used while creating the add-on, unless they are
commented out.

::

	// print_r($foo);

Whitespace in Files
===================

No whitespace can precede the opening PHP tag or follow the closing PHP
tag. Output is buffered, so whitespace in your files can cause output to
begin before CodeIgniter outputs its content, leading to errors and an
inability for CodeIgniter to send proper headers. In the examples below,
select the text with your mouse to reveal the incorrect whitespace.


Compatibility
=============

Unless specifically mentioned in your add-on's documentation, all code
must be compatible with PHP version 5.1+. Additionally, do not use PHP
functions that require non-default libraries to be installed unless your
code contains an alternative method when the function is not available,
or you implicitly document that your add-on requires said PHP libraries.

Class and File Names using Common Words
=======================================

When your class or filename is a common word, or might quite likely be
identically named in another PHP script, provide a unique prefix to help
prevent collision. Always realize that your end users may be running
other add-ons or third party PHP scripts. Choose a prefix that is unique
to your identity as a developer or company.

**INCORRECT**::

	class Email		pi.email.php
	class Xml		ext.xml.php
	class Import	mod.import.php

**CORRECT**::

	class Pre_email		pi.pre_email.php
	class Pre_xml		ext.pre_xml.php
	class Pre_import	mod.pre_import.php

Database Table Names
====================

Any tables that your add-on might use must use the 'exp\_' prefix,
followed by a prefix uniquely identifying you as the developer or
company, and then a short descriptive table name. You do not need to be
concerned about the database prefix being used on the user's
installation, as CodeIgniter's database class will automatically convert
'exp\_' to what is actually being used.

**INCORRECT**::

	email_addresses		// missing both prefixes
	pre_email_addresses	// missing exp_ prefix
	exp_email_addresses	// missing unique prefix

**CORRECT**::

	exp_pre_email_addresses

.. note:: Be mindful that MySQL has a limit of 64 characters for table
	names. This should not be an issue as table names that would exceed this
	would likely have unreasonable names. For instance, the following table
	name exceeds this limitation by one character. Silly, no?
	**exp_pre_email_addresses_of_registered_users_in_seattle_washington**

One File per Class
==================

Use separate files for each class your add-on uses, unless the classes
are *closely related*. An example of CodeIgniter files that contains
multiple classes is the Database class file, which contains both the DB
class and the DB_Cache class, and the Magpie plugin, which contains
both the Magpie and Snoopy classes.

Whitespace
==========

Use tabs for whitespace in your code, not spaces. This may seem like a
small thing, but using tabs instead of whitespace allows the developer
looking at your code to have indentation at levels that they prefer and
customize in whatever application they use. And as a side benefit, it
results in (slightly) more compact files, storing one tab character
versus, say, four space characters.

Line Breaks
===========

Files must be saved with Unix line breaks. This is more of an issue for
developers who work in Windows, but in any case ensure that your text
editor is setup to save files with Unix line breaks.

Code Indenting
==============

Use Allman style indenting. With the exception of Class declarations,
braces are always placed on a line by themselves, and indented at the
same level as the control statement that "owns" them.

**INCORRECT**::

	function foo($bar) {
		// ...
	}

	foreach ($arr as $key => $val) {
		// ...
	}

	if ($foo == $bar) {
		// ...
	} else {
		// ...
	}

	for ($i = 0; $i < 10; $i++)
		{
		for ($j = 0; $j < 10; $j++)
			{
			// ...
			}
		}
		
	try {
		// ...
	}
	catch() {
		// ...
	}

**CORRECT**::

	function foo($bar)
	{
		// ...
	}

	foreach ($arr as $key => $val)
	{
		// ...
	}

	if ($foo == $bar)
	{
		// ...
	}
	else
	{
		// ...
	}

	for ($i = 0; $i < 10; $i++)
	{
		for ($j = 0; $j < 10; $j++)
		{
			// ...
		}
	}
	
	try 
	{
		// ...
	}
	catch()
	{
		// ...
	}

Bracket and Parenthetic Spacing
===============================

In general, parenthesis and brackets should not use any additional
spaces. The exception is that a space should always follow PHP control
structures that accept arguments with parenthesis (declare, do-while,
elseif, for, foreach, if, switch, while), to help distinguish them from
functions and increase readability.

**INCORRECT**::

	$arr[ $foo ] = 'foo';

**CORRECT**::

	$arr[$foo] = 'foo'; // no spaces around array keys

**INCORRECT**::

	function foo ( $bar )
	{

	}

**CORRECT**::

	function foo($bar) // no spaces around parenthesis in function declarations
	{

	}

**INCORRECT**::

	foreach( $query->result() as $row )

**CORRECT**::

	foreach ($query->result() as $row) // single space following PHP control structures, but not in interior parenthesis

Localized Text
==============

Any text that is output in the control panel should use language
variables in your lang file to allow localization.

**INCORRECT**::

	return "Invalid Selection";

**CORRECT**::

	return $this->lang->line('invalid_selection');

Private Methods and Variables
=============================

Methods and variables that are only accessed internally by your class,
such as utility and helper functions that your public methods use for
code abstraction, should be prefixed with an underscore.

::

	convert_text()		// public method
	_convert_text()		// private method

PHP Errors
==========

Code must run error free and not rely on warnings and notices to be
hidden to meet this requirement. For instance, never access a variable
that you did not set yourself (such as $_POST array keys) without first
checking to see that it isset().

Make sure that while developing your add-on, error reporting is enabled
for ALL users, and that display_errors is enabled in the PHP
environment. You can check this setting with::

	if (ini_get('display_errors') == 1)
	{
		exit "Enabled";
	}

On some servers where display_errors is disabled, and you do not have
the ability to change this in the php.ini, you can often enable it with::

	ini_set('display_errors', 1);

**NOTE:** Setting the
`display_errors <http://us.php.net/manual/en/ref.errorfunc.php#ini.display-errors>`_
setting with ini_set() at runtime is not identical to having it enabled
in the PHP environment. Namely, it will not have any effect if the
script has fatal errors

Short Open Tags
===============

Always use full PHP opening tags, in case a server does not have
short_open_tag enabled.

**INCORRECT**::

	<? echo $foo; ?>

	<?=$foo?>

**CORRECT**::

	<?php echo $foo; ?>

One Statement Per Line
======================

Never combine statements on one line.

**INCORRECT**::

	$foo = 'this'; $bar = 'that'; $bat = str_replace($foo, $bar, $bag);

**CORRECT**::

	$foo = 'this';
	$bar = 'that';
	$bat = str_replace($foo, $bar, $bag);

Strings
=======

Always use single quoted strings unless you need variables parsed, and
in cases where you do need variables parsed, use braces to prevent
greedy token parsing. You may also use double-quoted strings if the
string contains single quotes, so you do not have to use escape
characters.

**INCORRECT**::

	"My String"					// no variable parsing, so no use for double quotes
	"My string $foo"				// needs braces
	'SELECT foo FROM bar WHERE baz = \'bag\''	// ugly

**CORRECT**::

	'My String'
	"My string {$foo}"
	"SELECT foo FROM bar WHERE baz = 'bag'"

SQL Queries
===========

MySQL keywords are always capitalized: SELECT, INSERT, UPDATE, WHERE,
AS, JOIN, ON, IN, etc.

Break up long queries into multiple lines for legibility, preferably
breaking for each clause.

**INCORRECT**::

	// keywords are lowercase and query is too long for
	// a single line (... indicates continuation of line)
	$query = $this->db->query("select foo, bar, baz, foofoo, foobar as raboof, foobaz from exp_pre_email_addresses
	...where foo != 'oof' and baz != 'zab' order by foobaz limit 5, 100");

**CORRECT**::

	$query = $this->db->query("SELECT foo, bar, baz, foofoo, foobar AS raboof, foobaz
					FROM exp_pre_email_addresses
					WHERE foo != 'oof'
					AND baz != 'zab'
					ORDER BY foobaz
					LIMIT 5, 100");

Default Function Arguments
==========================

Whenever appropriate, provide function argument defaults, which helps
prevent PHP errors with mistaken calls and provides common fallback
values which can save a few lines of code. Example::

	function foo($bar = '', $baz = FALSE)