set default value on array

Question

Is it possible to pass in an array to a function and return that same array object back out?

function array_setdefault($arr, $key, $dflt) {
    if (array_key_exists($key, $arr)) {
        return $arr[$key];
    }
    $arr[$key] = $dflt;
    return $arr[$key];
}

$errors = ["foo" => ["bar"]];
array_push(array_setdefault($errors, "foo", []), "bim");
array_push(array_setdefault($errors, "bla", []), "wub");

var_dump($errors);

leads to:

array(1) {
    ["foo"]=>
    array(1) {
        [0]=>
        string(3) "bar"
    }
}

but I'd like to have:

array(2) {
    ["foo"]=>
    array(2) {
        [0]=>
        string(3) "bar"
        [1]=>
        string(3) "bim"
    }
    ["bla"]=>
    array(1) {
        [0]=>
        string(3) "wub"
    }
}

I.e. $dflt should be set on the array for the $key in case it's not been set. If it has been set previously or after it's set in the current call to array_setdefault, return what's at $arr[$key] (that is, the $dflt array object).

Barmar · Accepted Answer · 2014-08-16 13:43:00Z

3

You need to use a reference argument so that changes in the function will modify the original variable, and also return a reference.

function &array_setdefault(&$arr, $key, $dflt) {
    if (!array_key_exists($key, $arr)) {
        $arr[$key] = $dflt;
    }
    return $arr[$key];
}

Putting & before the function name makes it return a reference. Putting & before a parameter makes that parameter a reference argument.

answered Aug 16, 2014 at 13:43

Barmar

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3 Comments

Rudie Over a year ago

By-ref as argument and as return value... That's going to go wrong at some point.

XORcist Over a year ago

Is there a comparable functionalit built into the language?

Barmar Over a year ago

I can't think of anything simple.

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