php: efficiently running functions with one-time l

问题:

after reading the responses I have rewritten my question.

Let's say I have a theoretical php application that uses objects that do different things. For every page that gets loaded by the application, different scripts will be run.

now I made a simple php script that creates a simple object. (this is all made up, I'm just trying to understand this before I code it)

$user = new userClass($db);
$user->login($credentials);

all is fine, and I can even repeat the procedure several times after creating the user class

$user = new userClass($db);
$user->login($credentials);
...
$user->login($credentials2);

now imagine if these 2 parts are split in 2 different php files.

file1:
$user = new userClass($db);
$user->login($credentials);
file2:
$user->login($credentials2);

include file1
include file2

if they are run in order all is fine, but if they are not, or if file1 is not included at all...

file2:
$user->login($credentials);
file1:
$user = new userClass($db);
$user->login($credentials2);

include file2
include file1

then it won't work... they have to maintain order, so lets make a main php file that gets loaded no matter what.

main file:
$user = new userClass($db);
file1:
$user->login($credentials);
file2:
$user->login($credentials2);

(included files with autoloading for example) include main include file1 include file2 or include main include file2 include file1 or include main include file2

now file1 and 2 can be loaded in any order, and one does not depend on the other, but what if both file1 or file2 are unnecessary?

main file:
$user = new userClass($db);
//nothing else gets loaded

then the main file is also unnecessary, and will prove to be a resource hog, sure if its one class it's no problem, but what if the main file loads hundreds of classes that never get used?

not elegant at all.

Then let's try to do it another way, let's scrap the main file completely and do it like this (below is the bare bone example of what I want to achieve):

file1:
if(!is_object($user)){
    $user = new userClass($db);
}
$user->login($credentials);
file2:
if(!is_object($user)){
    $user = new userClass($db);
}
$user->login($credentials2);

sure, it works, but it's not elegant, now is it?

let's try it with method overloading...

class loader {
   private $objects;
   private $db;
   function __construct($db){
      $this->objects = array();
      $this->db = $db;
   }
   function __get($name){
      if(!isset($this->objects[$name])){
         return $this->objects[$name] = new $name($this->db);
      }
   }
}

main file:
$loader = new loader($db);
file1:
$loader->user->login($credentials);
file3:
$loader->user->login($credentials3);
file2:
$loader->user->login($credentials2);
file4:
$loader->user->login($credentials4);

seems to work, until you realize that you can no longer give any of the objects that are created this way any other variable except $db. This means that loader class is limited to use with user class only (for example) because using loader class with any other class will require editing of the loader class

and a simple script like this:

$user = new userClass($this->db);
$user->login($credentials);
$form = new formClass($_POST);
$form->process($info);

will require 2 separate loader classes or at least 2 methods in the loader class

   class loader {
       private $objects;
       private $db;
       function __construct($db){
          $this->objects = array();
          $this->db = $db;
       }
       function getuserclass($name){
          if(!isset($this->objects[$name])){
             return $this->objects[$name] = new $name($this->db);
          }
       }
       function getformclass($name){
          if(!isset($this->objects[$name])){
             return $this->objects[$name] = new $name($_POST);//just an unrealistic example.
          }
       }
    }

main file:
$loader = new loader($db);
file1:
$loader->getuserclass('user')->login($credentials);
file3:
$loader->getformclass('form')->process($info);

but this is not elegant either.

How is this really supposed to be done?

回答1:

This would probably work for you:

class loader {
   private $objects;

   function __construct(){
      $this->objects = array();
   }

   function __call($name, $args){
      if(!isset($this->objects[$name])){
         return $this->objects[$name] = new $name($args);
      }
   }
}
$loader = new loader();

$user = $loader->user($db);
$form = $loader->form($form_args);

If you want multiple instances you could perhaps include an additional first argument in each call to loader that is a name, and change the loader code to use the first arg as a key for the object, and pass the rest to the object's constructor.

回答2:

imo, this is exactly why using include() through an app is a bad idea, and can create serious maintenance headaches. Especially for people who are unfamiliar with the code. They may open a PHP file two years from now and see a variable... and have no idea what it is or where it is initialized.

If you are encountering this sort of problem, your app's basic structure probably needs to be redone. a better way to organize your app is to put all includes at the top of your app, so that there's no ambiguity about what files are included, or the order that they are included. And then use a templating system to control output. Dont use 'includes()' to insert code inline. Use them instead more like C includes. Your included files should house functions and classes, and very little, if any code, that runs in the global scope.

Do that, and I think you'd find that you'll stop encountering these sort of problems.

回答3:

simply use the autoloader and singleton pattern: create a class where you put all your classes(for example /modules/ )with the same filename as the contained class,remember ONLY the declaration.

now include this code(on a "main file")on top of all your pages:

function __autoload($class_name) {
    if(!ctype_alnum(str_replace(array('-','_'), '',$class_name)))//filename check,security reasons
        die('Module name not valid! ');
    require_once 'modules/'.$class_name.'.php';//load the class
}

you may want to create a singleton class(it's a object pattern,it basically ensure that only 1 entity of the class exists)

file:UserClass.php

<?php
class UserClass{
    private static $istance=null;
    private function UserClass($db){
        //your constructor code here
    };
    private static function getIstance($db){//you can call it init($db) and create a getInstace() that only return the instance,i prefer that way,do as you want.
        if($istance==null)
            $istance=new UserClass($db);
        return $istance;
    };
    function login($credentials){
            //....
    }
    //...other functions...
}
?>

now to use it you can simply do like so:

require 'main.php';//require the autoloader
$user=UserClass::getIstance($db);//the class file will be automatically included and a new istance will be created
$user->login($credentials1);
$user->login($credentials2);
$user=UserClass::getIstance($db);//no new istance will be created,only returned
$user->login($credentials3);
$user2=UserClass::getIstance($db);//no new istance will be created,only returned
$user2->login($credentials4);

//Userclass($db);// don't use like that,it will give you ERROR(it's private like singleton pattern says)