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    1: Title:           Zend 2.0 Namespaces
    2: Version:         $Id: 002.txt,v 1.1.1.2 2012/05/29 12:34:36 misho Exp $
    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