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1.1       misho       1: Title:           Zend 2.0 Namespaces
1.1.1.2 ! misho       2: Version:         $Id: 7d7cb885d85b5ffc3f7e14171bb226b1e3c711a4 $
1.1       misho       3: Status:          declined
                      4: Maintainer:      Stig S. Bakken <ssb@php.net>
                      5: Created:         2001-09-08
                      6: Modified:        2001-09-08
                      7:                   
                      8: 
                      9: 1. Background/Need
                     10: ==================
                     11: 
                     12: PHP and Zend 1.0 have come to a point where a lot of reusable code is
                     13: being written; from simple functions and classes to entire application
                     14: frameworks.  It is becoming increasingly difficult to avoid symbol
                     15: name collisions with the current scoping methods.
                     16: 
                     17: The symbol scopes available in Zend 1.0 are the global scope, the
                     18: class scope and the function scope.  All scopes but classes may
                     19: contain variables, only the class and global scopes may contain
                     20: functions, while only the global scope may contain constants and
                     21: classes.  This means that all of Zend 1.0's scoping methods are
                     22: inherently limited for solving symbol name collision problems.
                     23: 
                     24: 
                     25: 2. Overview
                     26: ===========
                     27: 
                     28: Namespaces in Zend 2.0 provide a way to manage the symbol collision
                     29: problem by making it possible to define multiple symbol tables able to
                     30: contain all types of symbols.  Zend will get the notion of a current
                     31: namespace, defaulting to the current global one.  The current name
                     32: space may be changed on a file-by-file basis.  Symbols in other name
                     33: spaces than the current one may be referenced using a new namespace
                     34: operator.  It will be possible to "import" symbols from one namespace
                     35: into another.
                     36: 
                     37: 
                     38: 3. Functionality
                     39: ================
                     40: 
                     41: 3.1. Namespace Syntax
                     42: =====================
                     43: 
                     44: The namespace operator ":" is used to refer to symbols in other
                     45: namespaces than the current one:
                     46: 
                     47: Class:          Namespace:class
                     48: Function:       Namespace:function
                     49: Static method:  Namespace:class::method
                     50: Variable:       $Namespace:variable
                     51: Constant:       Namespace:CONSTANT
                     52: Class variable: $Namespace:class::variable
                     53: 
                     54: To refer to symbols in the global namespace, symbols are prefixed with
                     55: only the namespace operator:
                     56: 
                     57: Class:          :class
                     58: Function:       :function
                     59: Static method:  :class::method
                     60: Variable:       $:variable
                     61: Constant:       :CONSTANT
                     62: Class variable: $:class::variable
                     63: 
                     64: Note: $:variable will effectively be just another syntax for
                     65: $GLOBALS['variable'].
                     66: 
                     67: A namespace may have a name containing a ":", it is always the last
                     68: ":" character in the symbol qualifier that is the actual namespace
                     69: operator:
                     70: 
                     71: Class:          Name:Space:class
                     72: Function:       Name:Space:function
                     73: Static method:  Name:Space:class::method
                     74: Variable:       $Name:Space:variable
                     75: Constant:       Name:Space:CONSTANT
                     76: Class variable: $Name:Space:class::variable
                     77: 
                     78: (Here, the ":" between "Name" and "Space" is part of the name, it is
                     79: the one after "Space" that is the namespace operator.)
                     80: 
                     81: 
                     82: 3.2. Defining Namespaces
                     83: ========================
                     84: 
                     85: Individual files may define a namespace that will apply to the entire
                     86: file.  If no "namespace" operator occurs in the file, it will be in
                     87: the 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: 
                     98: Or 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: 
                    110: Code executed within the "HTML" namespace may refer to the Form class
                    111: as just "Form".  Code executed from within other namespaces has to
                    112: refer to it as "HTML:Form".  The "namespace" statement must occur
                    113: before 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: 
                    120: 3.3. Importing Symbols
                    121: ======================
                    122: 
                    123: It is possible to import symbols from another namespace into the
                    124: current 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: 
                    132: There is a potential for name clashes between symols of different
                    133: types that have the same qualifier syntax.  These are resolved in this
                    134: order: class, function, constant.
                    135: 
                    136: Optionally, the symbol type may be explicitly given to import (as
                    137: "class", "function", "variable" or "constant"):
                    138: 
                    139:   import class Form from HTML;
                    140: 
                    141: And finally, you may import all symbols of a given type:
                    142: 
                    143:   import constant * from HTML:Table;
                    144: 
                    145: The namespace with its symbols must already be defined before using
                    146: "import".
                    147: 
                    148: 
                    149: 4. Compatibility Notes
                    150: ======================
                    151: 
                    152: Old code that does not take advantage of namespaces will run without
                    153: modifications.
                    154: 
                    155: 
                    156: 5. Dependencies
                    157: ===============
                    158: 
                    159: The class variable syntax depends on this class variables being
                    160: implemented in the new ZE2 object model.
                    161: 
                    162: 
                    163: 6. Acknowledgements
                    164: ===================
                    165: 
                    166: Andi Gutmans <andi@zend.com> and Zeev Suraski <zeev@zend.com> for
                    167: initial ZE2 namespaces proposal
                    168: 
                    169: Dean Hall <php@apt7.com> for the initial symbol qualification syntax