1Title: Zend 2.0 Namespaces 2Version: $Id: 7d7cb885d85b5ffc3f7e14171bb226b1e3c711a4 $ 3Status: declined 4Maintainer: Stig S. Bakken <ssb@php.net> 5Created: 2001-09-08 6Modified: 2001-09-08 7 8 91. Background/Need 10================== 11 12PHP and Zend 1.0 have come to a point where a lot of reusable code is 13being written; from simple functions and classes to entire application 14frameworks. It is becoming increasingly difficult to avoid symbol 15name collisions with the current scoping methods. 16 17The symbol scopes available in Zend 1.0 are the global scope, the 18class scope and the function scope. All scopes but classes may 19contain variables, only the class and global scopes may contain 20functions, while only the global scope may contain constants and 21classes. This means that all of Zend 1.0's scoping methods are 22inherently limited for solving symbol name collision problems. 23 24 252. Overview 26=========== 27 28Namespaces in Zend 2.0 provide a way to manage the symbol collision 29problem by making it possible to define multiple symbol tables able to 30contain all types of symbols. Zend will get the notion of a current 31namespace, defaulting to the current global one. The current name 32space may be changed on a file-by-file basis. Symbols in other name 33spaces than the current one may be referenced using a new namespace 34operator. It will be possible to "import" symbols from one namespace 35into another. 36 37 383. Functionality 39================ 40 413.1. Namespace Syntax 42===================== 43 44The namespace operator ":" is used to refer to symbols in other 45namespaces than the current one: 46 47Class: Namespace:class 48Function: Namespace:function 49Static method: Namespace:class::method 50Variable: $Namespace:variable 51Constant: Namespace:CONSTANT 52Class variable: $Namespace:class::variable 53 54To refer to symbols in the global namespace, symbols are prefixed with 55only the namespace operator: 56 57Class: :class 58Function: :function 59Static method: :class::method 60Variable: $:variable 61Constant: :CONSTANT 62Class variable: $:class::variable 63 64Note: $:variable will effectively be just another syntax for 65$GLOBALS['variable']. 66 67A namespace may have a name containing a ":", it is always the last 68":" character in the symbol qualifier that is the actual namespace 69operator: 70 71Class: Name:Space:class 72Function: Name:Space:function 73Static method: Name:Space:class::method 74Variable: $Name:Space:variable 75Constant: Name:Space:CONSTANT 76Class variable: $Name:Space:class::variable 77 78(Here, the ":" between "Name" and "Space" is part of the name, it is 79the one after "Space" that is the namespace operator.) 80 81 823.2. Defining Namespaces 83======================== 84 85Individual files may define a namespace that will apply to the entire 86file. If no "namespace" operator occurs in the file, it will be in 87the global namespace: 88 89 1 namespace HTML; 90 2 91 3 class Form { 92 4 function Form() { 93 5 // constructor 94 6 } 95 7 // ... 96 8 } 97 98Or with the "nested" name syntax: 99 100 1 namespace HTML:Form; 101 2 102 3 class Image { 103 4 var $src; 104 5 function Image($src) { 105 6 $this->src = $src; 106 7 } 107 8 // ... 108 9 } 109 110Code executed within the "HTML" namespace may refer to the Form class 111as just "Form". Code executed from within other namespaces has to 112refer to it as "HTML:Form". The "namespace" statement must occur 113before any other statements in the file. 114 115# [ssb 2001-09-08]: 116# Should it be possible to "add" symbols to a namespace by including a 117# second file with the same namespace statement? 118 119 1203.3. Importing Symbols 121====================== 122 123It is possible to import symbols from another namespace into the 124current one with the "import" statement: 125 126 import * from HTML; // all symbols 127 128 import Form from HTML; // single symbols 129 130 import Form,Table from HTML; // multiple symbols 131 132There is a potential for name clashes between symols of different 133types that have the same qualifier syntax. These are resolved in this 134order: class, function, constant. 135 136Optionally, the symbol type may be explicitly given to import (as 137"class", "function", "variable" or "constant"): 138 139 import class Form from HTML; 140 141And finally, you may import all symbols of a given type: 142 143 import constant * from HTML:Table; 144 145The namespace with its symbols must already be defined before using 146"import". 147 148 1494. Compatibility Notes 150====================== 151 152Old code that does not take advantage of namespaces will run without 153modifications. 154 155 1565. Dependencies 157=============== 158 159The class variable syntax depends on this class variables being 160implemented in the new ZE2 object model. 161 162 1636. Acknowledgements 164=================== 165 166Andi Gutmans <andi@zend.com> and Zeev Suraski <zeev@zend.com> for 167initial ZE2 namespaces proposal 168 169Dean Hall <php@apt7.com> for the initial symbol qualification syntax 170
