PHP: How to access object inside class - php

Question

I have a language class with public data members:
class language {
public $error = "There was an error";
}
Then I have many different classes that uses this class. How can I access this class from within other classes? You could of course instantiate an object of it inside all the classes that uses it, but I suppose that would drastically decrease the performance, if I were to do that with multiple classes.
I do only need one object, since I don't change them anyway. So, I've done
$language = new language();
class name {
private $language;
public function __construct() {
global $language;
$this->language = $language;
}
public function method() {
mysql_query(...) or die($this->language->error);
}
}
Is this a good way to do it? Now I have to instantiate it in every "mother" script. And I suppose by doing __construct() I'm only passing a refrence, since I don't use the clone word?

Answer 1

Basically your language object is a dependency of your other objects. There are a number of factors you need to consider:
- performance (how wise it is to instantiate a new language object each time you need it, or whether that is even possible)
- testing - how you could test your classes if each one has a hard-coded dependency on your language class
- maintainability/readability.
There are various different solutions to the problem. The one that seems to be most in fashion in the PHP community is the Dependency Injection Container. This can be a good solution if you are in a greenfield situation.
A good article on the general subject is one by Martin Fowler (who else?).
EDIT: To explain a bit more the article deals with the Inversion of Control principle. I won't explain it in depth as I don't think I could do it as well as Martin Fowler amongst others but the nub of it is that your classes do not manage their own dependencies; that is done elsewhere (hence the name Inversion of Control). There are broadly two different ways of doing it - Dependency Injection (which may or may not involve a Container) and Service Locator. This section of Martin Fowler's article deals with some of the differences between the two.

Answer 2

I do only need one object
This is the Singleton pattern.
Here is a quick example of a way to have only one instance of your Language class:
class Language {
public $error = "text";
private static $instance = null;
public static function getInstance() {
if (self::$instance == null)
self::$instance = new self();
return self::$instance;
}
private function __construct() {}
}
$lang = Language::getInstance();
$text = $lang->error;
You can also use dependency injection:
interface ILanguage {
public function getError();
}
class Language implements ILanguage {
private $error = "error";
public function getError() {
return $this->error;
}
}
class name {
private $language;
public function __construct(ILanguage $lang) {
$this->language = $lang;
}
public function method() {
mysql_query(...) or die($this->language->getError());
}
}
$language = new Language();
$n = new name($language);
This example of dependency injection is called constructor injection.

Answer 3

Instantiate the Language object in the constructor of your class:
public function __construct() {
$this->language = new Language();
}

Answer 4

If you do not want to have instances of this class, consider making its properties and methods static:
class language {
static public $error = "There was an error";
}
then use them statically:
$error = language::$error;

Answer 5

Instead of using global variable, you could pass it via constructor.
public function __construct($language) {
$this->language = $language;
}