How to use a variable to address complex associative arrays in PHP

Question

Let's say I have the following multi-dimensional array:

$fruits['apple']['name'] = 'macintosh';

Is there any way of referencing the entire key path in a single variable?

I would like to somehow do the following:

$path = "['apple']['name']";
echo $fruits[$path];
//output would be "macintosh"

• user1299518: &references comes to my mind..
• Allen Liu: @vizvi Can you expand a bit on that? Thanks.
• user1299518: you could call: $fruits2 = &fruits['apple']; echo $fruits2['name']; would give "macintosh"
• goat: maybe interesting to you: stackoverflow.com/questions/8376602/… if you would like $fruits['apple/name'] to be valid
• Jared: You could always use classes instead of arrays.

Answer 1

Is there any way of referencing the entire key path in a single variable?

1) In a way like this: $fruits[$variable], the answer is no, there isn't.

Of course, there are several ways you can split a single $variable in two or more, and then use its parts separetely ($fruits[$part1][$part2])

This is a generic solution:

function get_path($array, $path)
{
 $value = $array;
 $parts = explode("']['", trim($path, "[']"));
 foreach($parts as $key)
 {
 $value = $value[$key];
 }
 return $value;
}
$fruits['apple']['name'] = 'macintosh';
$path = "['apple']['name']";
echo get_path($fruits, $path);
// output = 'macintosh'

---

2) As also pointed, you could use "eval", which is not recommended:

$fruits['apple']['name'] = 'macintosh';
$path = "['apple']['name']";
eval('echo $fruits' . $path . ';');
// output = 'macintosh'

---

3) Finally, if you want to access an element of the array using a reference variable, then simply:

$fruits['apple']['name'] = 'macintosh';
$path &= $fruits['apple']['name'];
echo $path; // output = 'macintosh'
$path = 'MSX';
echo $fruits['apple']['name']; // output = 'MSX'

Answer 2

There is obviously the horrible, never-to-be-used approach: eval()

But if you really want to do something like this, I would prefer something like this approach:

function &array_value_by_address (&$array, $address, $addressSeparator = '/') {
 $parts = explode($addressSeparator, $address);
 $thisLevel = array_shift($parts);
 if (isset($array[$thisLevel])) {
 if ($parts) {
 $ref = &array_value_by_address($array[$thisLevel], implode($addressSeparator, $parts));
 return $ref;
 } else {
 return $array[$thisLevel];
 }
 }
}

Because of the references in the function declaration, it's also possible to catch the return value in a variable and use it to modify the source array. This is optional - if you omit the & prefix at call time the caught value will simply be a copu and not a reference.

The caveat though - the function will return NULL if the "address" within the array does not exist, but there is no way to distinguish between this situation and a NULL value stored within the array.

See it working

Answer 3

J Brun's #3 answer is your best bet, however, his answer is not correct as he has demonstrated the bitwise-AND operator (&=) and not the referential assignment. This is the corrected code:

$fruits['apple'] = array( 'name' => 'macintosh' );
$path = &$fruits['apple']['name'];
echo $path; // outputs 'macintosh';

Answer 4

References might be what you need:

$path = &$fruits['apple']['name'];

Now every time you would access $path, it's the value of $fruits['apple']['name'] that will be used (or changed, etc.).

• Allen Liu: Thanks. I think this is the most promising answer so far for my case.

Answer 5

What you want to do is not directly possible - it would be ambigous if variables are chained.

You will need to write an accessor function such as

define('SEPARATOR','|');
function getElement($array,$path) {
 $path=explode(SEPARATOR,$path);
 $out=&$array;
 foreach ($path as $step) {
 if (!isset($out[$step])) return null;
 $out=$out[$step];
 }
 return $out;
}
$path="apple|name";
echo getElement($fruits,$path);