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Temporary Location for Coding Standards Review
The coding standards official location can be found in the Zend Framework Online Manual and are copied here for review and updates before being placed back into DocBook format in Subversion. The manual also contains translated versions that are not available here.

Table of Contents

Overview

Scope

This document provides the coding standards and guidelines for developers and teams working on or with the Zend Framework. The subjects covered are:

  • PHP File Formatting
  • Naming Conventions
  • Coding Style
  • Inline Documentation
  • Errors and Exceptions

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.

PHP File Formatting

General

For files that contain only PHP code, the closing tag ("?>") is to be omitted. It is not required by PHP, and omitting it prevents trailing whitespace from being accidentally injected into the output.

Important
Inclusion of arbitrary binary data as permitted by __HALT_COMPILER() is prohibited from any Zend framework PHP file or files derived from them. Use of this feature is only permitted for special installation scripts.

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 tab characters into the source code.

Maximum Line Length

The target line length is 80 characters; i.e., developers should aim keep code as close to the 80-column boundary as is practical. However, longer lines are acceptable. The maximum length of any line of PHP code is 120 characters.

Line Termination

Line termination is the standard way for Unix text files. 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

Abstractions Used in API (Class Interfaces)

When creating an API for use by application developers (as opposed to Zend Framework internal developers), if application developers must identify abstractions using a compound name, separate the names using underscores, not camelCase. For example, the name used for the MySQL PDO driver is 'pdo_mysql', not 'pdoMysql'. When the developer uses a string, normalize it to lowercase. Where reasonable, add constants to support this (e.g. PDO_MYSQL).

Classes

The Zend Framework employs a class naming convention whereby the names of the classes directly map to the directories in which they are stored. The root level directory of the Zend Framework is the "Zend/" directory, under which all classes are stored hierarchically.

Class names may only contain alphanumeric characters. Numbers are permitted in class names but are discouraged. Underscores are only permitted in place of the path separator. For example, the filename "Zend/Db/Table.php" must map to the class name "Zend_Db_Table".

If a class name is comprised of more than one word, the first letter of each new word must be capitalized. Successive capitalized letters are not allowed; e.g., a class "Zend_PDF" is not allowed, while "Zend_Pdf" is acceptable.

Zend Framework classes that are authored by Zend or one of the participating partner companies and distributed with the Framework must always start with "Zend_" and must be stored under the "Zend/" directory hierarchy accordingly.

These are examples of acceptable names for classes:

Important
Code that operates with the framework but is not part of the framework, such as code written by a framework end-user and not Zend or one of the framework's partner companies, must never start with "Zend_".

Interfaces

Interface classes must follow the same conventions as other classes (see above), but must end with "_Interface", such as in these examples:

Filenames

For all other files, only alphanumeric characters, underscores, and the dash character ("-") are permitted. Spaces are prohibited.

Any file that contains any PHP code must end with the extension ".php". These examples show the acceptable filenames for containing the class names from the examples in the section above:

File names must follow the mapping to class names described above.

Functions and Methods

Function names may only contain alphanumeric characters. Underscores are not permitted. Numbers are permitted in function names but are discouraged.

Function names must always start with a lowercase letter. When a function name consists of more than one word, the first letter of each new word must be capitalized. This is commonly called the "studlyCaps" or "camelCaps" method.

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

These are examples of acceptable names for functions:

For object-oriented programming, accessors for object members should always be prefixed with either "get" or "set". When using design patterns, such as the Singleton or Factory patterns, the name of the method should contain the pattern name where practical to make the pattern more readily recognizable.

Though function names may not contain the underscore character, class methods that are declared as protected or private must begin with a single underscore, as in the following example:

Functions in the global scope, or "floating functions," are permitted but discouraged. It is recommended that these functions be wrapped in a class and declared static.

Functions or variables declared with a "static" scope in a class generally should not be "private", but protected instead. Use "final" if the function should not be extended.

Variables

Variable names may only contain alphanumeric characters. Underscores are not permitted. Numbers are permitted in variable names but are discouraged.

For class member variables that are declared with the private or protected construct, the first character of the variable name must be a single underscore. This is the only acceptable usage of an underscore in a variable name. Member variables declared as "public" may never start with an underscore. For example:

Like function names, variable names must always start with a lowercase letter and follow the "camelCaps" capitalization convention.

Verbosity is encouraged. Variable names should always be as verbose as practical. Terse variable names such as "$i" and "$n" are discouraged for anything other than the smallest loop contexts. If a loop contains more than 20 lines of code, variables for such indices or counters need to have more descriptive names.

Constants

Constants may contain both alphanumeric characters and the underscore. Numbers are permitted in constant names.

Constant names must always have all letters capitalized.

To enhance readability, words in constant names must be separated by underscore characters. For example, "EMBED_SUPPRESS_EMBED_EXCEPTION" is permitted but "EMBED_SUPPRESSEMBEDEXCEPTION" is not.

Constants must be defined as class members by using the "const" construct. Defining constants in the global scope with "define" is permitted but discouraged.

Coding Style

PHP Code Demarcation

PHP code must always be delimited by the full-form, standard PHP tags (although you should see the note about [the closing PHP tag]):

Short tags are never allowed.

Strings

String Literals

When a string is literal (contains no variable substitutions), the apostrophe or "single quote" must always used to demarcate the string:

String Literals Containing Apostrophes

When a literal string itself contains apostrophes, it is permitted to demarcate the string with quotation marks or "double quotes". This is especially encouraged for SQL statements:

The above syntax is preferred over escaping apostrophes.

Variable Substitution

Variable substitution is permitted using either of these two forms:

For consistency, this form is not permitted:

String Concatenation

Strings may be concatenated using the "." operator. A space must always be added before and after the "." operator to improve readability:

When concatenating strings with the "." operator, it is permitted to break the statement into multiple lines to improve readability. In these cases, each successive line should be padded with whitespace such that the "." operator is aligned under the "=" operator:

Arrays

Numerically Indexed Arrays

Negative numbers are not permitted as array indices.

An indexed array may be started with any non-negative number, however this is discouraged and it is recommended that all arrays have a base index of 0.

When declaring indexed arrays with the array construct, a trailing space must be added after each comma delimiter to improve readability:

It is also permitted to declare multi-line indexed arrays using the array construct. In this case, each successive line must be padded with spaces such that beginning of each line aligns as shown below:

Associative Arrays

When declaring associative arrays with the array construct, it is encouraged to break the statement into multiple lines. In this case, each successive line must be padded with whitespace such that both the keys and the values are aligned:

Classes

Class Declarations

Classes must be named by following the naming conventions.

The brace is always written on the line underneath the class name ("one true brace" form).

Every class must have a documentation block that conforms to the phpDocumentor standard.

Any code within a class must be indented the standard indent of four spaces.

Only one class is permitted per PHP file.

Placing additional code in a class file is permitted but discouraged. In these files, two blank lines must separate the class from any additional PHP code in the file.

This is an example of an acceptable class declaration:

Class Member Variables

Member variables must be named by following the variable naming conventions.

Any variables declared in a class must be listed at the top of the class, prior to declaring any functions.

The var construct is not permitted. Member variables always declare their visibility by using one of the private, protected, or public constructs. Accessing member variables directly by making them public is permitted but discouraged in favor of accessor methods having the set and get prefixes.

Functions and Methods

Function and Method Declaration

Functions and class methods must be named by following the naming conventions.

Methods must always declare their visibility by using one of the private, protected, or public constructs.

As for classes, the opening brace for a function or method is always written on the line underneath the function or method name ("one true brace" form). There is no space between the function or method name and the opening parenthesis for the arguments.

This is an example of acceptable class method declarations:

Please note
Passing function or method arguments by reference is only permitted by defining the reference in the function or method declaration, as in the following example:

Call-time pass by-reference is prohibited.

The return value must not be enclosed in parentheses. This can hinder readability and can also break code if a function or method is later changed to return by reference.

Function and Method Usage

Function arguments are separated by a single trailing space after the comma delimiter. This is an example of an acceptable function call for a function that takes three arguments:

Call-time pass by-reference is prohibited. Arguments to be passed by reference must be defined in the function declaration.

For functions whose arguments permit arrays, the function call may include the "array" construct and can be split into multiple lines to improve readability. In these cases, the standards for writing arrays still apply:

Control Statements

If / Else / Elseif

Control statements based on the "if", "else", and "elseif" constructs must have a single space before the opening parenthesis of the conditional, and a single space between the closing parenthesis and opening brace.

Within the conditional statements between the parentheses, operators must be separated by spaces for readability. Inner parentheses are encouraged to improve logical grouping of larger conditionals.

The opening brace is written on the same line as the conditional statement. The closing brace is always written on its own line. Any content within the braces must be indented four spaces.

For "if" statements that include "elseif" or "else", the formatting must be as in these examples:

PHP allows for these statements to be written without braces in some circumstances. The coding standard makes no differentiation and all "if", "elseif", or "else" statements must use braces.

Use of the "elseif" construct is permitted but highly discouraged in favor of the "else if" combination.

Switch

Control statements written with the "switch" construct must have a single space before the opening parenthesis of the conditional statement, and also a single space between the closing parenthesis and the opening brace.

All content within the "switch" statement must be indented four spaces. Content under each "case" statement must be indented an additional four spaces.

The construct "default" may never be omitted from a "switch" statement.

Please note
It is sometimes useful to write a "case" statement which falls through to the next case by not including a "break" or "return". To distinguish these cases from bugs, such "case" statements must contain the comment "// break intentionally omitted".

Inline Documentation

Documentation Format

All documentation blocks ("docblocks") must be compatible with the phpDocumentor format. Describing the phpDocumentor format is beyond the scope of this document. For more information, visit http://phpdoc.org.

All source code file written for the Zend Framework or that operates with the framework must contain a "file-level" docblock at the top of each file and a "class-level" docblock immediately above each class. Below are examples of such docblocks.

To avoid losing track of @todo}}s in the source code, either use only an issue in our issue tracker, or include the issue identifier (e.g., ZF-123) in the {{@todo. This allows {{@todo}}s to be tracked and monitored the same as any other issue. It also makes {{@todo}}s more visible to the community, and helps find volunteers.

The sharp, '#', character should not be used to start comments.

Files

Every file that contains PHP code must have a header block at the top of the file that contains these phpDocumentor tags at a minimum:

Classes

Every class must have a docblock that contains these phpDocumentor tags at a minimum:

Functions

Every function, including object methods, must have a docblock that contains at a minimum:

  • A description of the function
  • All of the arguments
  • All of the possible return values
  • If a function/method may throw an exception, use "@throws"
Please note
It is not necessary to use the "@access" tag because the access level is already known from the "public", "private", or "protected" construct used to declare the function.

Require / Include

If a component uses another component, then the using component is responsible for loading the other component. If the use is conditional, then the loading should also be conditional.

If the file(s) for the other component should always load successfully, regardless of input, then use PHP's require_once statement.
If the file(s) loaded are variable dependent (e.g., require_once $userSelectedLogger), then use Zend::loadClass(), or wrap the require_once statement to throw an helpful exception on failure.

The include, include_once, require, and require_once statements should not use parentheses.

Errors and Exceptions

The Zend Framework codebase must be E_STRICT compliant. This means that all Zend Framework code must never emit PHP errors that would be reported in user scripts having error_reporting set to E_ALL | E_STRICT. See http://www.php.net/errorfunc for information on E_STRICT.

Zend Framework code should not emit PHP errors, if it is reasonably possible. Instead, throw meaningful exceptions. Zend Framework components have Exception class derivatives specifically for this purpose:

It is considered best practice within framework component code that exceptions are instantiated through the traditional new constructor method.

Some concern was raised about scripts that incur overhead by loading exception classes that are by definition only used in exceptional cases. When an application's performance requirements are such that this overhead is an issue, one should use either of two solutions:

  • Load the exception class in a traditional manner, and run the application in an environment that uses a PHP bytecode cache. A bytecode cache reduces the overhead of loading and parsing PHP classes that have been used in the environment earlier.
  • Lazy-load the exception class inside the code block where the exception is thrown. For example:

Reasonable care should be taken to avoid throwing exceptions except when genuinely appropriate. In general, if a Zend Framework component is asked to perform a duty that it cannot perform in a certain situation (e.g., illegal input, cannot read requested file), then throwing an exception is a sensible course of action. Conversely, if a component is able to perform its requested duty, despite some variance from expected input, then the component should continue with its work, rather than throw an exception.

Exception best practices

  • Use specific derived exceptions in both throw and catch. See the following two items:
  • Avoid throwing the Exception base class, or other exception superclass. The more specific the exception, the better it communicates to the user what happened.
  • Avoid catching the Exception base class, or other exception superclass. If a try block might encounter more than one type of exception, write a separate catch block for each specific exception, not one catch block for an exception superclass.
  • Some classes may require you to write more than one derived exception class. Write as many exception classes as needed, to distinguish between different types of situations. For example, "invalid argument value" is different from, "you don't have a needed privilege." Create different exceptions to identify different cases.
  • Don't put important diagnostic information only in the text of the exception method. Create methods and members in derived exception classes as needed, to provide information to the catch block. Create an exception constructor method that takes appropriate arguments, and populate the members of the class with those arguments.
  • Don't silently suppress exceptions and allow execution to continue in an erroneous state. If you catch an exception, either correct the condition or throw a new exception.
  • Keep implementation-specific exceptions isolated to the appropriate layer of your application. For instance, don't propagate SQLException out of the data layer code and into business layer code.
  • Don't use exceptions as a mechanism of flow control, or to return valid return values from a function.
  • Clean up resources such as database connections or network connections. PHP does not support a finally block as some programming languages do, so either clean up in the catch blocks, or else design flow control outside the catch block to perform cleanup, and let execution continue after the catch.
  • Use documentation from other languages for other best practices regarding using exceptions. Many of the principles are applicable, regardless of the language.

PHP Extensions

Zend Framework components may use a PHP extension only if the extension is available. If the extension can be disabled, Zend Framework code that uses it must check for availability of the extension, and fail appropriately if the extension is not available. This may consist of offering alternate code to provide similar or partial functionality, or else throwing an exception with a message explaining that certain functionality is not available without the extension being enabled.

Zend Framework components may use an extension only if that extension is enabled by default in the PHP.net binary distribution supported by the current release of Zend Framework. For instance, if Zend Framework 0.6.0 is intended to work with PHP 5.1.4 through 5.2.0, then the extension must be available in the default binary distribution for those versions of PHP.

Here is information about which extensions are enabled by default in different binary distributions of PHP on Windows:

Extension PHP 5.1.4 PHP 5.1.5 PHP 5.1.6 PHP 5.2.0 Zend Core
bcmath  
calendar  
com_dotnet
ctype
date
dom
filter      
ftp  
hash
iconv
json      
libxml
mysql    
odbc  
openssl        
pcre
PDO
Reflection
session
SimpleXML
SPL
standard
tokenizer  
wddx
xml
xmlreader
xmlwriter
Zend Accelerator  
Zend Core  
Zend Debugger  
Zend Optimizer  
zlib

The use of PHP's iconv functions are permitted and encouraged, when needed and appropriate. For example: $cleanedUTF8 = iconv("UTF-8", "UTF-8//IGNORE", $badUTF8);

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