Laravel error when using dynamic class names returned by method

Question

In Laravel (4 & 5), I am trying to use dynamic class names and then call them directly, but receiving a fatal error if not first storing them in a local string variable.

Assuming I have a basic class:

class SimpleModel {
     private $modelName;

     function __construct($id) {

        $this->modelName = AnotherModel::getName($id);

    }
}

Within the methods, I can easily do

$modelName = $this->modelName;
$modelName::find(1);

But I get a fatal error when trying the following:

$this->modelName::find(1);

This triggers a Symfony\Component\Debug\Exception\FatalErrorException with a message of

syntax error, unexpected &#039;::&#039; (T_PAAMAYIM_NEKUDOTAYIM)

Basically the T_PAAMAYIM_NEKUDOTAYIM is a syntax error generated from the :: symbol.

Can't wrap my head around why Laravel (or PHP in general) allows dynamic class names when using a local variable (within a method) but not a class variable.

I also tried putting it in a seprate method getModelName() method but getting the same error.

$this->getModelName()::find(1);

Instanciating a new class every time (new $this->modelName) is not a good solution.

I was looking into using PHP's Reflection but not sure how to do it without instanciating a new class every time. Since it is working when using a local string, it seems as Reflection might be an over kill.

Fabian Schmengler · Accepted Answer · 2015-08-27 11:31:24Z

2

This is due to how the PHP parser works (up to PHP 5). The T_PAAMAYIM_NEKUDOTAYIM token (::) is only allowed after T_STRING (that represents a class name, not a string within quotes) or, since PHP 5.3, T_VARIABLE.

But your code will work in PHP 7, where the parser has been fundamentally reworked (see: https://wiki.php.net/rfc/abstract_syntax_tree)

Demo: https://3v4l.org/sdBss

answered Aug 27, 2015 at 11:31

Fabian Schmengler

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1 Comment

dev7 Over a year ago

Thanks for explaining this.

jedrzej.kurylo · Accepted Answer · 2015-07-03 21:01:09Z

1

You can use call_user_func or call_user_func_array to call method of a class, the name of which is stored in object's attribute:

call_user_func(array($this->modelName, 'find'), 1)

OR

call_user_func_array(array($this->modelName, 'find'), array(1))

answered Jul 3, 2015 at 21:01

jedrzej.kurylo

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3 Comments

dev7 Over a year ago

That works, but still doesn't explain why this is happening. Any idea?

C3roe Over a year ago

Because it’s simply not supported.

jedrzej.kurylo Over a year ago

Since PHP 5.3 it is allowed to call static methods and access static attributes using dynamic class names stored in variables, e.g.: $a::foo(), but it stiill doesn't allow what you're trying to do. It's also not clear to me what benefit you see in calling static methods such unusual way.

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