What is going on with PHP type conversion between array and object

Question

When I Do this:

<?php

$object = array(
    'key' => 'value',
    1 => 'value',
    '11' => 'value',
    '22' => 'value'
);

print_r($object); echo'<br>';

$object = (object)$object;

print_r($object); echo'<br>';echo'<br>';

//ok looks good so far but then

echo $object->key       . '<br>'; // good
echo $object->{1}       . '<br>'; // bad 
echo $object->{11}      . '<br>'; // bad
echo $object->{'22'}    . '<br>'; // bad

$object->key = 'changed value';
$object->{1} = 'changed value';
$object->{'11'} = 'changed value';
$object->{'22'} = 'changed value';

echo'<br>'; print_r($object); echo'<br>';echo'<br>';

echo $object->key       . '<br>'; // good
echo $object->{1}       . '<br>'; // good 
echo $object->{11}      . '<br>'; // good
echo $object->{'22'}    . '<br>'; // good

$object = (array)$object;

echo'<br>'; print_r($object);echo'<br>';echo'<br>';

echo $object['key']     . '<br>'; // good
echo $object[1]         . '<br>'; // wtf 
echo $object['11']      . '<br>'; // wtf
echo $object['22']      . '<br>'; // wtf    
?>

I get this as result:

Array           ( [key] => value [1] => value [11] => value [22] => value ) 
stdClass Object ( [key] => value [1] => value [11] => value [22] => value ) 

value
Notice: Undefined property: stdClass::$1 in C:\Users\wl\Documents\USBWebserver v8.5\USBWebserver v8.5\8.5\root\Client\test.php on line 19
Notice: Undefined property: stdClass::$11 in C:\Users\wl\Documents\USBWebserver v8.5\USBWebserver v8.5\8.5\root\Client\test.php on line 20
Notice: Undefined property: stdClass::$22 in C:\Users\wl\Documents\USBWebserver v8.5\USBWebserver v8.5\8.5\root\Client\test.php on line 21


stdClass Object ( [key] => changed value [1] => value [11] => value [22] => value [1] => changed value [11] => changed value [22] => changed value ) 

changed value
changed value
changed value
changed value

Array ( [key] => changed value [1] => value [11] => value [22] => value [1] => changed value [11] => changed value [22] => changed value ) 

changed value
value
value
value

Is this a bug in PHP why is this happening. How can A array Or object have 2 equal keys with different values!?

Community · Accepted Answer · 2017-05-23 12:21:08Z

5

Update:

NikiC provided me an answer, it's explained here: The Symtable

Basically, arrays store numeric keys as integers, objects store numeric keys as strings. But when you do an array-to-object or object-to-array cast that constraint is not enforced.

array (size=7)
  'key' => string 'changed value' (length=13)
  1 => string 'value' (length=5)
  11 => string 'value' (length=5)
  22 => string 'value' (length=5)
  '1' => string 'changed value' (length=13)
  '11' => string 'changed value' (length=13)
  '22' => string 'changed value' (length=13)

That's not correct; e.g. 11 is integer and '11' is a string (two different keys).

Use var_dump instead of print_r, as it shows type.

I suggest you try with this script:

<?php

$object = array(
  'key' => 'value',
  1 => 'value',
  '11' => 'value',
  '22' => 'value'
);

$object = (object) $object;

var_dump($object);

$object->key = 'changed value';
$object->{1} = 'changed value';
$object->{'11'} = 'changed value';
$object->{'22'} = 'changed value';

$object = (array) $object;

var_dump($object);

There are certainly some oddities here, but you can't expect to get good results because variables starting with integer are illegal.

edited May 23, 2017 at 12:21

CommunityBot

11 silver badge

answered Oct 17, 2013 at 13:30

Dejan Marjanović

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3 Comments

botenvouwer Over a year ago

I did not claim that this was oop, but fine. This php behavior is really unsuspected. Why is this not generating a fatal error. How can a array still contain object properties. And of course the other way around. Object with array values. Its just a php wtf.

Dejan Marjanović Over a year ago

@sirwilliam wtf or not, look here 3v4l.org/V6lD1#v500, it sort of makes sense. wasn't trying to offend, sorry.

Dejan Marjanović Over a year ago

@sirwilliam I've updated the answer with answer I got from PHP core engineer.

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