array_walk trying to write to outside array

Question

I have a simple piece of code that isn't working as I would expect it would, could someone please explain why it isn't populating the fields array and how to solve it.

$fields = [];

array_walk($class->properties, function($v, $k) use ($fields) {
    $fields[] = $v->name;
});

die(var_dump($fields));

// output is []

Pass by reference in the use, not by value: array_walk($class->properties, function($v, $k) use (&$fields){$fields[] = $v->name;}); — Mark Baker
– Mark Baker, Commented Aug 11, 2017 at 21:40
worth pointing out for this usecase, the function array_map would have been a better choice. — user3791372
– user3791372, Commented Aug 11, 2017 at 21:53

localheinz · Accepted Answer · 2017-08-11 22:14:08Z

5

Use this:

$fields = [];

array_walk($class->properties, function($v, $k) use (&$fields) {
    $fields[] = $v->name;
});

die(var_dump($fields));

After I wrote this I saw Mark Baker comment. That's the right answer.

For reference, see:

http://php.net/manual/en/language.references.pass.php

edited Aug 11, 2017 at 22:14

localheinz

9,6422 gold badges37 silver badges44 bronze badges

answered Aug 11, 2017 at 21:42

Felippe Duarte

15.2k2 gold badges27 silver badges29 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

localheinz · Accepted Answer · 2017-08-11 22:16:41Z

1

Alternatively, you can use array_map():

$fields = array_map(function($v) {
    return $v->name;
}, $class->properties);

die(var_dump($fields));

For reference, see:

http://php.net/manual/en/function.array-map.php

answered Aug 11, 2017 at 22:16

localheinz

9,6422 gold badges37 silver badges44 bronze badges

Comments

Community · Accepted Answer · 2023-11-21 15:10:29Z

The following code demonstrates a class whose sole property properties contains an array of objects, each of which has a name property, as follows:

<?php

$class = new stdClass;
$class->properties = [new stdClass,new stdClass, new stdClass];

$class->properties[0]->name = "Anne";
$class->properties[1]->name = "Bob";
$class->properties[2]->name = "Robin";

$fieldsA = [];
$fieldsB = [];

if ( array_walk( $class->properties, function( $o ) use ( &$fieldsA ){ 
                                      $fieldsA[] = $o->name;
                                    }) ) {
   echo "\nMission accomplished:\n";
   var_dump($fieldsA);
}

$fieldsB = array_map(  function( $e ) {
                                      return $e->name;
                                      },$class->properties);
if (count($fieldsB) > 0) {
   echo "\nMission accomplished:\n";
   var_dump( $fieldsB );
}

See live code

As you may note, both array_walk() and array_map() will produce the same results of stuffing a new array with the names that the three objects contain. Array_map() offers more simplicity than array_walk() which requires a use variable and a reference operator. Also, the return value of array_map() is a brand new array if all goes well. So, I concur with @localheinz and recommend it as the better choice.

Note: regarding the callback, it is unnecessary to specify value, key parameters. Both of these built-in functions examine each element of properties. Specifying function( $v, $k ) would be helpful if the code needed to do something with an element's key.

Collectives™ on Stack Overflow

array_walk trying to write to outside array

3 Answers 3

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related