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PHP pass function name as param then call the function?

Posted by: admin April 23, 2020 Leave a comment

Questions:

I need to pass a function as a parameter to another function and then call the passed function from within the function…This is probably easier for me to explain in code..I basically want to do something like this:

function ($functionToBeCalled)
{
   call($functionToBeCalled,additional_params);
}

Is there a way to do that.. I am using PHP 4.3.9

Thanks!

How to&Answers:

I think you are looking for call_user_func.

An example from the PHP Manual:

<?php
function barber($type) {
    echo "You wanted a $type haircut, no problem";
}
call_user_func('barber', "mushroom");
call_user_func('barber', "shave");
?>

Answer:

In php this is very simple.

<?php

function here() {
  print 'here';
}


function dynamo($name) {
 $name();
}

//Will work
dynamo('here');
//Will fail
dynamo('not_here');

Answer:

function foo($function) {
  $function(" World");
}
function bar($params) {
  echo "Hello".$params;
}

$variable = 'bar';
foo($variable);

Additionally, you can do it this way. See variable functions.

Answer:

You could also use call_user_func_array(). It allows you to pass an array of parameters as the second parameter so you don’t have to know exactly how many variables you’re passing.

Answer:

I know the original question asked about PHP 4.3, but now it’s a few years later and I just wanted to advocate for my preferred way to do this in PHP 5.3 or higher.

PHP 5.3+ now includes support for anonymous functions (closures), so you can use some standard functional programming techniques, as in languages like JavaScript and Ruby (with a few caveats). Rewriting the call_user_func example above in “closure style” would look like this, which I find more elegant:

$barber = function($type) {
    echo "You wanted a $type haircut, no problem\n";
};

$barber('mushroom');
$barber('shave');

Obviously, this doesn’t buy you much in this example – the power and flexibility comes when you pass these anonymous functions to other functions (as in the original question). So you can do something like:

$barber_cost = function($quantity) {
    return $quantity * 15;
};

$candy_shop_cost = function($quantity) {
    return $quantity * 4.50;   // It's Moonstruck chocolate, ok?
};

function get_cost($cost_fn, $quantity) {
    return $cost_fn($quantity);
}

echo '3 haircuts cost $' . get_cost($barber_cost, 3) . "\n";
echo '6 candies cost $' . get_cost($candy_shop_cost, 6) . "\n";

This could be done with call_user_func, of course, but I find this syntax much clearer, especially once namespaces and member variables get involved.

One caveat: I’ll be the first to admit I don’t know exactly what’s going on here, but you can’t always call a closure contained in a member or static variable, and possibly in some other cases. But reassigning it to a local variable will allow it to be invoked. So, for example, this will give you an error:

$some_value = \SomeNamespace\SomeClass::$closure($arg1, $arg2);

But this simple workaround fixes the issue:

$the_closure = \SomeNamespace\SomeClass::$closure;
$some_value = $the_closure($arg1, $arg2);

Answer:

If you need pass function with parameter as parameter, you can try this:

function foo ($param1){
   return $param1;
}

function bar ($foo_function, $foo_param){
    echo $foo_function($foo_param);
}

//call function bar
bar('foo', 'Hi there');  //this will print: 'Hi there'

phpfiddle example

Hope it’ll be helpful…

Answer:

If you want to do this inside a PHP Class, take a look at this code:

// Create a sample class
class Sample
{

    // Our class displays 2 lists, one for images and one for paragraphs
    function __construct( $args ) {
        $images = $args['images'];
        $items  = $args['items'];
        ?>
        <div>
            <?php 
            // Display a list of images
            $this->loop( $images, 'image' ); 
            // notice how we pass the name of the function as a string

            // Display a list of paragraphs
            $this->loop( $items, 'content' ); 
            // notice how we pass the name of the function as a string
            ?>
        </div>
        <?php
    }

    // Reuse the loop
    function loop( $items, $type ) {
        // if there are items
        if ( $items ) {
            // iterate through each one
            foreach ( $items as $item ) {
                // pass the current item to the function
                $this->$type( $item ); 
                // becomes $this->image 
                // becomes $this->content
            }
        }
    }

    // Display a single image
    function image( $item ) {
        ?>
        <img src="<?php echo $item['url']; ?>">
        <?php 
    }

    // Display a single paragraph
    function content( $item ) {
        ?>
        <p><?php echo $item; ?></p>
        <?php 
    }
}

// Create 2 sample arrays
$images = array( 'image-1.jpg', 'image-2.jpg', 'image-3.jpg' );
$items  = array( 'sample one', 'sample two', 'sample three' );

// Create a sample object to pass my arrays to Sample
$elements = { 'images' => $images, 'items' => $items }

// Create an Instance of Sample and pass the $elements as arguments
new Sample( $elements );