Is there a way to reassign $this?

问题:

First of all, I do not want to extend a class. I would ideally like to do this.

public function __construct() {
 /* Set Framework Variable */
 global $Five;
 $this =& $Five;
}

I have a system where the variable $Five is a container class which contains other libraries. I could assign this to a local variable of Five... i.e.

public function __construct() {
 /* Set Framework Variable */
 global $Five;
 $this->Five = $Five;
}

However, the reason why I am trying to avoid this is that function calls would be getting a little long.

$this->Five->load->library('library_name');

Its a little ugly. Far better would be.

$this->load->library('library_name');

What is the best solution for this?

回答1:

I think that

$this->Five->load->library('library_name');

is going to be your best option unless you decide to have the class extend the helper class. AKA

class Something extends Helper_Class

However, this means that Helper_Class is instantiated every time you instantiate a class.

---

Another method would be to have a pseudo-static class that assigned all of the helper classes to class members

public function setGlobals($five)
{
    $this->loader = $five->loader;
}

Then just call it

public function __construct($five)
{
    someClass::setGlobals($five);
}

---

If $Five is a global, you could just global $Five everytime you want to use it, but putting that at the top of every function just seems like bad coding.

---

Also, I'd just like to do my public service announcement that Global variables are generally a bad idea, and you might want to search 'Dependency Injection' or alternative to globals. AKA

public function __construct($five);

instead of

global $five;

Globals rely on an outside variable to be present and already set, while dependency injection requests a variable that it is assuming to be an instance of the Five class.

If you are running PHP 5.1 (Thanks Gordon), you can insure the variable is an instance of the FiveClass by doing this:

public function__construct(FiveClass $five);

回答2:

$this is a reference to the current instance of the class you are defining. I do not believe you can assign to it. If Five is a global you ought to be able to just do this:

$Five->load->library('library_name');

回答3:

You might wanna go with some kind of implementation of the dependency injection pattern:

Dependency injection (DI) in computer programming refers to the process of supplying an external dependency to a software component. It is a specific form of inversion of control where the concern being inverted is the process of obtaining the needed dependency.

See also the documentation for the symfony DI container. I can highly recommend this DI container implementation if you want to improve the way you handle your 'globals'.

You could also have a read of this question on 'best ways to access global objects'.

回答4:

How about making the relevant data members and methods of Five static class members? This

$this->Five->load->library('library_name');

would become this

Five::load->library('library_name');

and you wouldn't have to pass &$Five around everywhere.

回答5:

You cannot overwrite $this (like e.g. in C++) but you can easily build an aggregate using __call() for method calls and __get(), __set(), __isset() for properties.

Example for __call():

class Five {
  public function bar() {
    echo __METHOD__, " invoked\n";
  }
}

class Foo {
  protected $Five = null;

  public function __construct(Five $five=null) {
     if ( is_object($five) ) {
       $this->Five = $five;
     }
   }

  public function __call($name, $args) {
    // there's no accessible method {$name} in the call context
    // let's see if there is one for the object stored in $five
    // and if there is, call it.
    $ctx = array($this->Five, $name);
    if ( !is_null($this->Five) && is_callable($ctx) ) {
      return call_user_func_array($ctx, $args);
    }
    else {
      // ....
    }
  }
}

$foo = new Foo(new Five);
$foo->bar();

prints Five::bar invoked.
In my opinion the biggest draw back is that it is much harder to see "from the outside" what the object is capable of.

回答6:

I'm pretty sure you can't reassign $this, as it's one of those special things that looks like a variable in PHP, but is treated slightly differently behind the scenes.

If your concerns are the semantics of your method calling getting too long, I'd make load a method call instead of an object property

$this->load()->library('library_name');

public function load()
{
    return $this->Five;
}

回答7:

maybe better for you will be to use PHP Magic Methods? http://www.php.net/manual/en/language.oop5.overloading.php#language.oop5.overloading.methods