- 1 Overview
- 2 PHP File Formatting
- 3 Naming Conventions
- 4 Coding Style
- 4.1 PHP Code Demarcation
- 4.2 Strings
- 4.2.1 String Literals
- 4.2.2 String Literals Containing Apostrophes
- 4.2.3 Variable Substitution
- 4.2.4 String Concatenation
- 4.3 Arrays
- 4.4 Classes
- 4.5 Functions and Methods
- 4.6 Control Statements
- 4.7 Inline Documentation
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
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.
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.
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 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 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.
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_".
Interface classes must follow the same conventions as other classes (see above), but must end with "_Interface", such as in these examples:
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.
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.
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 function 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 may contain both alphanumeric characters and the underscore. Numbers are permitted in constant names.
Constant names must always have all letters capitalized.
To enhance readiblity, 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.
PHP code must always be delimited by the full-form, standard PHP tags:
Short tags are never allowed.
When a string is literal (contains no variable substitutions), the apostrophe or "single quote" must always used to demarcate the string:
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 is permitted using either of these two forms:
For consistency, this form is not permitted:
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:
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 multiline 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:
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 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 any additional PHP code in the file.
This is an example of an acceptable class declaration:
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 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:
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 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 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.
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.
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".
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.
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:
Every class must have a docblock that contains these phpDocumentor tags at a minimum:
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
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.
If a function/method may throw an exception, use "@throws":