Dynamically Create Functions with Eval() in PHP

Question

I'm trying to create functions dynamically with eval(). But I get this warning: Notice: Use of undefined constant Any suggestion?

$funcs = array('func_a', 'func_b', 'func_c');
foreach($funcs as $func_name) {
    eval( 'function ' . $func_name . '() { 
            mainfunc(' . $func_name . '); 
        }' 
    );  
}

func_a();
func_b();
func_c();

function mainfunc($func_name) {
    echo $func_name . '<br />';
}

Assuming the array $func is an option value stored in a database and I need the function names for a callback function in a separate part of the script. So creating anonymous functions with create_function() is not what I'm looking for.

Thanks for your info.

In the line mainfunc(' . $func_name . ');, you need to wrap $func_name in quotes. As it stands now, that line turns to mainfunc(func_a);. — user1233508
– user1233508, Commented Sep 19, 2012 at 6:01
take a look over here also; stackoverflow.com/questions/12438521/… — Tom
– Tom, Commented Sep 19, 2012 at 6:05
I don't think it's necessary to create function dynamically in such case. — xdazz
– xdazz, Commented Sep 19, 2012 at 6:08
To those who don't see the necessity of it, there are cases which need to pass function names to a custom function which expects a function name in the parameter as a call-back function, like add_action() in WordPress. When creating action hooks to schedule background processes in WordPress based on unique Ids, creating dynamic functions based on the saved ID becomes useful. Hope it makes sense. — Teno
– Teno, Commented Sep 19, 2012 at 6:16

Glavić · Accepted Answer · 2012-09-19 08:50:34Z

4

Use better approach than eval(), it is called overloading.

Example:

class MainFunc {

    public function __call($name, $arguments)
    {
        echo "_call($name)<br>";
    }

    public static function __callStatic($name, $arguments)
    {
        echo "_callStatic($name)<br>";
    }

}

# php >= 5.4.x
(new MainFunc)->func_a();
(new MainFunc)->func_b("param", "param2");
# or php < 5.4
$mainFunc = new MainFunc;
$mainFunc->func_a();
$mainFunc->func_b("param", "param2");

MainFunc::func_a_static();
MainFunc::func_b_static("param", "param2");

Output is:

_call(func_a)
_call(func_b)
_callStatic(func_a_static)
_callStatic(func_b_static)

edited Sep 19, 2012 at 8:50

answered Sep 19, 2012 at 6:30

Glavić

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3 Comments

Teno Over a year ago

Interesting, thanks for your input. Just my PHP version does not support the callStack() method.

Glavić Over a year ago

Then do not use __callStatic(). I have just demonstrated both possible solutions.

Teno Over a year ago

__call() seems to be the way to go. Thanks.

jimp · Accepted Answer · 2012-09-19 06:05:40Z

2

Your eval body needs to read:

mainfunc(\'' . $func_name . '\');

Without the single quotes, eval() makes code that has an unquoted literal--an undefined constant.

answered Sep 19, 2012 at 6:05

jimp

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Comments

Teno · Accepted Answer · 2012-09-19 10:59:51Z

For those who were wondering what I was talking about, here is the sample WordPress plugin which demonstrates how dynamic function creation comes handy.

/* Plugin Name: Sample Action Hooks with Dynamic Functions */

// assuming this is an option retrieved from the database
$oActions = array(  'a' => array('interval' => 10, 'value' => 'hi'),
                    'b' => array('interval' => 30, 'value' => 'hello'),
                    'c' => array('interval' => 60, 'value' => 'bye')
            );  

add_action('init', LoadEvents);
function LoadEvents() {
    global $oActions;
    foreach($oActions as $strActionName => $array) {
        eval( 'function ' . $strActionName . '() { 
                    SampleEvents(\'' . $strActionName . '\'); 
                }' 
        );  
        add_action('sampletask_' . md5($strActionName), $strActionName);
        if (!wp_next_scheduled( 'sampletask_' . md5($strActionName)))
            wp_schedule_single_event(time() + $oActions[$strActionName]['interval'], 'sampletask_' . md5($strActionName));                  
    }
}
function SampleEvents($strActionName) {
    global $oActions;
    // just log for a demo
    $file = __DIR__ . '/log.html';
    $current = date('l jS \of F Y h:i:s A') . ': ' . $strActionName . ', ' . $oActions[$strActionName]['value'] . '<br />' . PHP_EOL;
    file_put_contents($file, $current, FILE_APPEND);    
    wp_schedule_single_event(time() + $oActions[$strActionName]['interval'], 'sampletask_' . md5($strActionName));
}

And the same functionality could be achieved with __call().

/* Plugin Name: Sample Action Hooks */

add_action('init', create_function( '', '$oSampleEvents = new SampleEvents;' ));
class SampleEvents {
    public $oActions = array(   'a' => array('interval' => 10, 'value' => 'hi'),
                                'b' => array('interval' => 30, 'value' => 'hello'),
                                'c' => array('interval' => 60, 'value' => 'bye')
                        );
    function __construct() {                
        foreach($this->oActions as $strActionName => $arrAction) {
            add_action('sampletask_' . md5($strActionName), array(&$this, $strActionName));
            if (!wp_next_scheduled( 'sampletask_' . md5($strActionName)))
                wp_schedule_single_event(time() + $this->oActions[$strActionName]['interval'], 'sampletask_' . md5($strActionName));
        }
    }
    function __call($strMethodName, $arguments) {
        // just log for a demo
        $file = __DIR__ . '/log.html';
        $current = date('l jS \of F Y h:i:s A') . ': ' . $strMethodName . ', ' . $this->oActions[$strMethodName]['value'] . '<br />' . PHP_EOL;
        file_put_contents($file, $current, FILE_APPEND);    
        wp_schedule_single_event(time() + $this->oActions[$strMethodName]['interval'], 'sampletask_' . md5($strMethodName));
    }
}

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