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!

What version of php are you using? I think you are required to use php 5.3 to use a variable for the class name to access a static variable within that class. — racerror
– racerror, Commented Jan 4, 2010 at 17:55

Victor Nicollet · Accepted Answer · 2010-01-04 17:52:49Z

28

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

answered Jan 4, 2010 at 17:52

Victor Nicollet

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5 Comments

Peter Bailey Over a year ago

"frobnicate" is my new favorite word.

Mark A. Nicolosi Over a year ago

Okay, I'm trying to access a static variable, so it looks like I'll need PHP 5.3. Thanks.

Victor Nicollet Over a year ago

I shouldn't be giving this advice, since eval is evil... but you can with appropriate precautions use eval('return '.$class.'::$fields;') to get that static variable. Or use a static function instead. :)

Mark A. Nicolosi Over a year ago

That's exactly what I ended up doing. Agreed on the evilness, though ;)

Juha Palomäki Over a year ago

Since PHP 5.5 you can also use the "class" static member to access the fully qualified name, for example Account::class. See: php.net/manual/en/…

Ali · Accepted Answer · 2017-01-28 01:08:53Z

1

I have also experienced receiving such Fatal Error: Class 'MyClass' not found when you're class has a specific namespace, then it's probably the namespacing. You need to also mention the namespace in your String variable.

$class = "App\MyClass"; // mention the namespace too
$instance = new $class();

edited Jan 28, 2017 at 1:08

answered Dec 1, 2015 at 11:17

Ali

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Comments

yfeldblum · Accepted Answer · 2010-01-04 17:53:04Z

0

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

answered Jan 4, 2010 at 17:53

yfeldblum

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1 Comment

Mark A. Nicolosi Over a year ago

I get what T_PAAMAYIM_NEKUDOTAYIM. The wiki article doesn't explain why I can't do the above.

Pascal MARTIN · Accepted Answer · 2010-01-04 17:57:17Z

0

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

edited Jan 4, 2010 at 17:57

answered Jan 4, 2010 at 17:49

Pascal MARTIN

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2 Comments

Mark A. Nicolosi Over a year ago

I'm actually using inside of of a static class function, but it doesn't work if I pass the class name either.

Pascal MARTIN Over a year ago

@Mark : yes ; it's because you cannot do something like $className::$data with PHP < 5.3 ;; it's only possible with PHP >= 5.3

hktang · Accepted Answer · 2016-10-21 07:41:17Z

-1

I find this similar line works in my Laravel app:

$thing->all(new Account);

answered Oct 21, 2016 at 7:41

hktang

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Comments

Jimmy Shelter · Accepted Answer · 2010-01-04 17:55:58Z

-2

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?

edited Jan 4, 2010 at 17:55

answered Jan 4, 2010 at 17:47

Jimmy Shelter

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2 Comments

Mark A. Nicolosi Over a year ago

I don't think that's it - it doesn't work if I pass the class name either.

racerror Over a year ago

self does exist in php. self refers to the current objects class type for use in static context.

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