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
• CodeSniffer Testbed

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.

PHP File Formatting

General

For PHP files 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.

Also using the closing tag to generate HTML output within a method is omitted. Instead use heredoc syntax if needed.

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.

The code following a opening brace must be indented 4 additional spaces.

Multiple assignments must have the same indentation.

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:

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 not allowed in function names.

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 "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 heavily 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.

The opening brace of functions and methods has to be in the next line.

Optional Parameters

Use "null" as the default value instead of "false", for situations like this:

public function foo($required, $optional = null)

when $optional does not have or need a particular default value.

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 may only contain alphanumeric characters. Underscores or numbers are not permitted.

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 heavily discouraged.

Booleans and the NULL Value

Unlike PHP's documentation, the Zend Framework uses lowercase for both boolean values and the "null" value.

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 only allowed within view scripts.

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 and each value 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 heavily discouraged. In these files, a blank line 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.

Following the more common usage in the PHP developer community, static methods should declare their visibility first:

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:

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.

The use of type hinting is encouraged where possible with respect to the component design. For example,

Where possible, try to keep your use of exceptions vs. type hinting consistent, and not mix both approaches at the same time in the same method for validating argument types. However, before PHP 5.2, "Failing to satisfy the type hint results in a fatal error," and might fail to satisfy other coding standards involving the use of throwing exceptions. Beginning with PHP 5.2, failing to satisfy the type hint results in an E_RECOVERABLE_ERROR, requiring developers to deal with these from within a custom error handler, instead of using a try..catch block.

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 not allowed 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.

Global

Usage of the global keyword is not allowed. Use $GLOBALS[xxx] instead.

Inline Documentation

General

All docblock parts are compatible with the phpDocumentor format and must follow the following standard.
Docblocks start always with /*. The use of / or // is only allowed for comments within functions.

A docblock must contain a short description and minimum one parameter.

Optionally a long description and multiple parameters can be added.

Indenting

All docblock parts which are not keywords have to be under each other with the same indenting.

Also when describing parameters the keywords, parameters, and description have to have the same indenting to be under each other.

File Header

Each file which is delivered with the Zend Framework must have the following header block:

When other filestypes are used like *.SH, *.BAT, *.JS and so on, the header block must also be contained as header comment. Only when a filetype does not support comments like *.CSS the header block can be omited. The clauses must be added in the above seen order.

The @package clause has to be the component which this file is part of it, for example Zend_Db or Zend_Gdata. There are only two exceptions:
All demo files are located in the component Demos and all classes in the incubator have to be handled as if they are in core... so "incubator/Zend/Class" becomes the component "Zend_Class".
There must exist exact one @package clause per header.

The @subpackage clause has to be a logical separation within this component. Logical separations occur when there are several directories which seperate parts of the same component. The component name if contained in the separation has to be omitted. For example a file which is in Zend/Db/Adapters/* will have Adapters as separation and Zend_Db as component. Only files which are in the main directory of the framework which is "Zend" can omit the subpackage. There must exist maximum one @subpackage clause per header.

The @copyright clause has to include the actual year of the release of the framework.

If this file contains a depreciated class it must have the optional @depreciated clause.

Require Once

All classes/files which are required must contain a @see clause:

Class/Interface Header

A class or interface must have a class header looking like this:

The clauses must be added in the above seen order.

The short discription explains what this class does. It must not extend one single line.

The long descriptive text can be ommitted if there is no need for it.

The @package clause has to contain the component which this file is part of it, for example Zend_Db or Zend_Gdata.

The @subpackage clause has to contain a logical separation within this component. Logical separations occur when there are several directories which seperate parts of the same component. For example a file which is in Zend/Db/Adapters/* will have "Zend_Db_Adapters" as separation. There is only one exception: All files which are part of the demos directory have to be in the Demos subpackage. Only files which are in the main directory of the framework which is "Zend" can omit the subpackage.

The @uses clause has to contain the extended or implemented classname. A class which "extends Zend_MyClass" must have a clause @uses Zend_MyClass. Also a class which "implementes Zend_MyClass" must have a clause @uses Zend_MyClass. When multiple classes or interfaces are used, you must include a @uses clause for every class or interface. When no class is extended or interface is implemented then the @uses clause must be ommitted.

The @see clause is optional and can be added to link to another component within the framework. You can add multiple clauses.

The @since clause can be added optionally to include the version since which this class is available. It must include the complete version number of the framework. Only one since clause is allowed to be added.

The @copyright clause has to include the actual year of the release of the framework.

If this file contains a depreciated class it must have the optional @depreciated clause in the same format as the @since clause.

Function Header

Each function must have a function header.
The header has to look like this:

All parameters of the function must be available.
The following types are allowed:

• boolean
• integer
• float
• string
• array
• Zend_xxx (must be an existing class of the framework)
• false
• true
• null

If more than one type could be used then the possible types have to be seperated with "|" like show above.

If a parameter can be omitted the description must prepend a (optional) like shown above.

A @since clause can be added to show since when this function is available. Only one clause is allowed.

The @see clause can be added to link to another component which describes functionallity of this method, or which is used by this method. Multiple clauses are allowed. Every clause must contain only one class link.

If the function can throw an exception the @throws clause must be declared.
Multiple exception types must be seperated with "|". Also a description must be added why the exception is thrown.

A @return clause must always be defined. Only for class constructor and destructor the @return clause must be ommitted.
If multiple types can be returned the types must be seperated with "|".
An description can be appended, but is not necessary.
If the class itself is returned (fluid interface) then the description

must be added.

If the function does not return any value then the return value must be set to void

Inline Documentation

Documentation within a method is good practice and should be done to increase readability of the code.

The only acceptable syntax is phpdoc ("/*") or pearl ("//").
The usage of the ("#") or the ("/**") Syntax is not allowed.

Errors and Exceptions

The Zend Framework codebase must be E_STRICT compliant. Zend Framework code should not emit PHP warning (E_WARNING, E_USER_WARNING), notice (E_NOTICE, E_USER_NOTICE), or strict (E_STRICT) messages when error_reporting is 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.

Exceptions must be lazy loaded before they are thrown:

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.

CodeSniffer Testbed

The complete framework is tested with a coding standard which we have written using PHP_CodeSniffer. Several existing tests have been reused and others have been rewritten to allow automatic testing of the above written coding standard.
In some points the CodeSniffer tests are more restrictive than the written standard to make the code more readable and consistent.