Coding style

This is a new draft of the coding guidelines that I'm working on. The structure was based on the Zend guidelines and our old Coding page.

Overview

Scope

This document describes coding standards and guidelines for developers working on or with Moodle.

Goals

Good coding standards are important in any development project, particularly when multiple developers are working on the same project. Having coding standards helps to ensure that the code is of high quality, has fewer bugs, and is easily maintained.

Abstract goals we strive for:

• extreme simplicity
• tool friendliness, such as use of method signatures, constants, and patterns that support IDE tools and auto-completion of method, class, and constant names.

When considering the goals above, each situation requires an examination of the circumstances and balancing of various trade-offs.

Note that much of the existing Moodle code may not follow all of these guidelines - we continue to upgrade this code when we see it.

File Formatting

PHP tags

Always use "long" php tags. However, to avoid whitespace problems, DO NOT include the closing tag at the very end of the file.

<?php

   include('config.php');

Indentation

Use an indent of 4 spaces with no tab characters. Editors should be configured to treat tabs as spaces in order to prevent injection of new tab characters into the source code.

Maximum Line Length

Aim for 80 characters if it is convenient. However, you can go longer if it helps overall readability. The maximum line length is 120 characters.

Line Termination

Use standard Unix text format. Lines must end only with a linefeed (LF). Linefeeds are represented as ordinal 10, or hexadecimal 0x0A.

Do not use carriage returns (CR) like Macintosh computers (0x0D).

Do not use the carriage return/linefeed combination (CRLF) as Windows computers (0x0D, 0x0A).

Lines should not contain trailing spaces. In order to facilitate this convention, most editors can be configured to strip trailing spaces, such as upon a save operation.

Naming Conventions

Filenames

Filenames should :

• be whole english words
• be as short as possible
• use lowercase letters only
• end in .php, .html, .js, or .xml

Classes

Class names should always be lowercase english words, separated by underscores:

class some_custom_class {

   function class_method() {
       echo "foo";
   }

}

Functions and Methods

Function names should be simple English lowercase words, and start with the name of the module to avoid conflicts between modules. Words should be separated by underscores.

Verbosity is encouraged: function names should be as illustrative as is practical to enhance understanding.

Note there is no space between the function name and the following (brackets).

function forum_set_display_mode($mode=0) {

   global $USER, $CFG;
        
   if ($mode) {
       $USER->mode = $mode;
   } else if (empty($USER->mode)) {
       $USER->mode = $CFG->forum_displaymode;
   }

}

Function Parameters

Parameters are always simple lowercase English words (sometimes more than one, like $initialvalue), and should always have sensible defaults if possible.

Use "null" as the default value instead of "false", for situations like this where a default value isn't needed. public function foo($required, $optional = null)

However, if an optional parameter is boolean, and its logical default value should be true, or false, then using true or false is acceptable.

Variables

Variable names should always be easy-to-read, meaningful lower-case English words. If you really need more than one word then run them together, but keep them short as possible. Use plural names for arrays of objects.

    GOOD: $quiz
    GOOD: $errorstring
    GOOD: $assignments (for an array of objects)
    GOOD: $i (but only in little loops)

    BAD: $Quiz
    BAD: $aReallyLongVariableNameWithoutAGoodReason
    BAD: $error_string

Constants

Constants should always be in upper case, and always start with the name of the module. They should have words separated by underscores. define("FORUM_MODE_FLATOLDEST", 1);

Booleans and the NULL Value

Use lower case for true, false and null.

Coding Style

Strings

Since performance is not such an issue in current versions of PHP, the main criteria with strings is readability.

Single quotes

Always use single quotes when a string is literal, or contains a lot of double quotes (like HTML):

$a = 'Example String'; echo ''; $html = '<a href="http://something" title="something">Link</a>';

Double quotes

These are a lot less useful in Moodle.

Use double quotes when you need to include plain variables or a lot of single quotes. In Moodle 2.0 or later you won't need to be doing a lot of single quotes for SQL so that's not an issue.

echo "$string"; $statement = "You aren't serious!";