PHP passing a class name becomes a string when passed to a function

Question

Here's what I want to do:

public function all($model) {
  $query = 'SELECT ' . implode(', ', $model::$fields) ....;
}

Called like this:

$thing->all(Account);

I get this error:

Parse error: syntax error, unexpected T_PAAMAYIM_NEKUDOTAYIM in /home/mark/public_html/*/account.php on line 15

When inspecting $model with var_dump it turns out its a string. In the the first example if I change $model to Account on the $query line it works fine.

How can a take a string and turn it back into a class?

Edit: Updated example and title to reflect the problem isn't with self.

Solution: Since I'm not using PHP5.3, I had to resort to using eval() to get what I wanted. Thanks everybody!

Answer 1

Try '$this' instead of self.

Self does work this way in PHP. PHP thinks it encounters an unknown constant, which it can't find, and then it assumes it's a string containing 'self'.

Edit: Can you post the class and the code where you instantiate the object?

Answer 2

You cannot use self this way : it can only be used in a static context (i.e. inside a static method) to point to the class -- and not its name.

If you are working with non-static methods (seems you are), you should use $this, instead of self.

Actually, before PHP 5.3, you cannot use a static method/data with a "dynamic" (i.e contained in a variable) class name -- see the examples on the page Static Keyword : they only work with PHP 5.3, for that kind of manipulation.

Which means a portion of code like this one :

class ClassA {
    public static $data = 'glop';
}

$className = 'ClassA';
var_dump($className::$data);

Will not work with PHP < 5.3

Answer 3

Classes are not first-class citizens in PHP, as such they may not be stored in variables, passed as function arguments, or returned from functions.

However, PHP will let you simulate a first-class citizen by using a string containing the name of the class, in certain situations:

$class = "Account";

$instance = new $class(); // You can create instances

call_user_func(array($class, 'frobnicate')); // You can call static functions

That's about all in PHP < 5.3. However, with PHP 5.3, you can also:

$class::frobnicate(); // cleanly call static functions

$fields = $class::$fields; // access static variables

Answer 4

See Wikipedia on the scope resolution operator. Especially see the section on PHP and Hebrew.