unset a element of an array via reference

Question

I can access anywhere inside the multi-dimensional an array via reference method. And I can change the its value. For example:

$conf = array(
    'type' => 'mysql',
    'conf' => array(
            'name' => 'mydatabase',
            'user' => 'root',
            'pass' => '12345',
            'host' => array(
                    '127.0.0.1',
                    '88.67.45.123',
                    '129.34.123.55'
            ),
            'port' => '3306'
    )
);

$value = & $this->getFromArray('type.conf.host');
$value = '-- changed ---';

// result
$conf = array(
    'type' => 'mysql',
    'conf' => array(
            'name' => 'mydatabase',
            'user' => 'root',
            'pass' => '12345',
            'host' => '-- changed ---'
            'port' => '3306'
    )
);

BUT, I can't destroy the that section:

// normally success
unset($conf['type']['conf']['host']);

// fail via reference
$value = & $this->getFromArray('type.conf.host');
unset($value);

Is there a solution?

Answer 1

Ok, better answer I think. In order to unset , you should get a reference to the container array, then unset the element within the array;

i.e.

$value = & $this->getFromArray('type.conf');

unset  $value['host'];

Answer 2

References are not like hard-links. If you unset a reference, this will not unset the origin value.

<?php 
$a = 5;
xdebug_debug_zval('a'); // a: (refcount=1, is_ref=0), int 5

$b = &$a;
xdebug_debug_zval('a'); // a: (refcount=2, is_ref=1), int 5
xdebug_debug_zval('b'); // b: (refcount=2, is_ref=1), int 5

unset($b);
xdebug_debug_zval('a'); // a: (refcount=1, is_ref=0), int 5

Why not write a little Config class which abstracts the data (array)? Since objects are always passed by reference you won't need to handle this at your own.

class Config
{
    // ...
}

$config = new Config(array(
    'db' => array(
        'name' => 'mydatabase',
        'user' => 'root',
        'pass' => '12345',
    )
));

$config->get('db.user');
$config->set('db.user', 'newuser');
$config->unset('db.user');
//...

Answer 3

Here is my function for unsetting nested keys

public function unsetKey(string $dotSeparatedKey)
{
    $keys = explode('.', $dotSeparatedKey);
    $pointer = &$this->data;
    $current = false; // just to make code sniffer happy
    // we traverse all but the last key
    while (($current = array_shift($keys)) && (count($keys) > 0)) {
        // if some key is missing all the subkeys will be already unset
        if (!array_key_exists($current, $pointer)) {
            // is already unset somewhere along the way
            return;
        }
        // set pointer to new, deeper level
        // called for all but last key
        $pointer = &$pointer[$current];
    }
    // handles empty input string
    if ($current) {
        // we finally unset what we wanted
        unset($pointer[$current]);
    }
}

Answer 4

Creating some functions for my framework, think they halp you.

1. Function set value in array using reference for navigation
- if reference ending by name/key, this name/key will be equal setting value
- if reference ending by delimiter, last name/key will be array with setting value

function array_reference_set($input_arr=array(),$reference='',$delimiter='->',$set_var=''){
    switch ($reference){
        case (is_string($reference)):
            $reference = array_reverse(explode($delimiter, $reference),true);
            break;
        case (!is_array($reference)):
            return $input_arr;
    }
    $key = array_pop($reference);
    if (count($reference)<1){
        if($key!=''){
            $input_arr[$key] = $set_var;
        }elseif (!is_array($input_arr) && $key==''){
            $input_arr = array($set_var);
        }elseif ($key==''){
            $input_arr[] = $set_var;
        }
    }else{
        if (!is_array($input_arr)){
            $input_arr = array($key=>array());
        }
        if (isset($input_arr[$key])){
            $input_arr[$key] = $this->array_reference_set($input_arr[$key],$reference,$delimiter,$set_var);
        }else{
            $input_arr[$key] = $this->array_reference_set(array(),$reference,$delimiter,$set_var);
        }
    }
    return $input_arr;
}

$arr = array_reference_set(array(),'a->b->c','->','test');
//equal
$arr = array('a'=>array('b'=>array('c'=>'test')));//or
$arr['a']['b']['c'] = 'test';

$arr = array_reference_set(array(),'a->b->c->','->','test');
//equal
$arr = array('a'=>array('b'=>array('c'=>array('test'))));//or
$arr['a']['b']['c'][] = 'test';

2. Function set unset value from array using reference

- if reference ending is delimiter, then will be unset varible with name/key befor delimiter
- one moment of using this function: you need update array by returned result of function (in the end of code example)

function array_reference_unset($input_arr=array(),$reference='',$delimiter='->'){
    switch ($reference){
        case (is_string($reference)):
            $reference = array_reverse(explode($delimiter, $reference),true);
            break;
        case (!is_array($reference)):
            return $input_arr;
    }
    $key = array_pop($reference);
    if (count($reference)<1 && is_string($key)){
        if ($key!=''){
            unset($input_arr[$key]);
        }else{
            return false;
        }
    }else{
        if (isset($input_arr[$key])){
            $ret = $this->array_reference_unset($input_arr[$key],$reference,$delimiter);
            if ($ret!==false){
                $input_arr[$key] = $ret;
            }else{
                unset ($input_arr[$key]);
            }
        }
    }
    return $input_arr;
}

$arr = array('a'=>array('b'=>array('c'=>'test')));// test subject

$arr = array_reference_unset($arr,'a->b->c','->');//and
$arr = array_reference_unset($arr,'a->b->c->','->');
//equal
unset($arr['a']['b']['c']);

p.s. sorry for my pure English