How to change data of reference passed Array in Closure

Question

I have an Eventbus that takes a filter name as its first parameter and a Closure as second parameter. Like this:

$this->EventBus->subscribe('FilterTestEvent', function(){/*Do Something*/});

It's called like this:

$filteredValue = $this->EventBus->filter('FilterTestEvent', $anyValue);

What I want now is to pass an array as reference to the Closure that then is changed in any way (here: add elements) and then return something as the filtered value:

$item_to_change = array('e1' => 'v1', 'e2' => 'v2');

$this->EventBus->subscribe('FilterTestEvent', function(&$item){
    $item['new'] = 'LoremIpsum';

    return true;
});
    
$filtered = $this->EventBus->filter('FilterTestEvent', $item_to_change);

Now I would a print_r($item_to_change) expect to look like the following:

Array
(
    [e1] => v1
    [e2] => v2
    [new] => LoremIpsum
)

But instead it looks like the original array:

Array
(
    [e1] => v1
    [e2] => v2
)

The eventbus internally stores all closures and calls them if needed through call_user_func_array() with the closure as first argument and the value as the only argument array element.

How can I achieve what it's meant to do?

sybear · Accepted Answer · 2013-12-20 12:27:24Z

0

Probably this line:

$filtered = $this->EventBus->filter('FilterTestEvent', $item_to_change);

is supposed to return a new filtered array, not modify the original one.

So check it:

print_r($filtered);

Passing by reference is possible by modifying a function (adding &):

function filter(&$array){  //Note & mark
  $array['new_index'] = "Something new" ;
}

$array = array("a"=> "a");
filter($array); //The function now receives the array by reference, not by value.
var_dump($array); //The array should be modified.

Edit:

Make your callback return the filtered array:

$this->EventBus->subscribe('FilterTestEvent', function(&$item){
    $item['new'] = 'LoremIpsum';

    return $item ;
});

Passing by reference should not work here, because in the source code that $value variable is swapped with another value and returned after.

edited Dec 20, 2013 at 12:27

answered Dec 20, 2013 at 12:02

sybear

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9 Comments

fsebwas Over a year ago

Actually the $filtered's value should now be set to true since this is what the filter returns. Yeah, you're right. But the closure does that already.

fsebwas Over a year ago

What docs do you mean? The Eventbus source code? -- A link is included above.

sybear Over a year ago

You should find what function FilterTestEvent does and returns. But filter function for sure does not accept array by reference.

sybear Over a year ago

Oh wait, let me see some more.

sybear Over a year ago

Need more source code, preferably some class related to EventBus. We need to see what exactly function is responsible for filtering. I see only class Event.

|

Aaron Bertrand · Accepted Answer · 2025-08-30 23:28:30Z

0

Ok. I found the answer. The filter function needs to be changed so that it accepts arrays as value, in which I can save the reference. For details see difference Revision 1 and Revision 2 of the Eventbus source code.

edited Aug 30 at 23:28

Aaron Bertrand

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answered Dec 21, 2013 at 13:36

fsebwas

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