Attempt to retrieve nested key array value given unkown amount of supplied keys into PHP function

Question

I would like to supply a function with an array of keys (unknown quantity) and a value to then set the corresponding nested array value (using those keys and value). I know how to do this for retrieval, just not for assigning. For retrieval, I do:

function test($keys, $value){
    $arr = ["key1" => ["key2" => true], "key3" => true];

    $nestedArrayValue = $arr;
    foreach($keys as $key){
        $nestedArrayValue = $arr[$key];
    }

    return $nestedArrayValue;
}

But when assigning a value, that $nestedArrayValue is a copy, so it won't actually change the $arr. Likewise, if I were to pass by reference where $nestedArrayValue = &$arr, the foreach would override the entire $arr each time. For example:

function test($keys, $value){
    $arr = ["key1" => ["key2" => true], "key3" => true];

    $nestedArrayValue = &$arr;
    foreach($keys as $key){
        $nestedArrayValue = $arr[$key];
    }

    $nestedArrayValue = $value;

    var_dump($arr);
}

test(["key1", "key2"], "test value");
//OUTPUT:
string(10) "test value" 

The entire $arr gets overridden (which it should). My question is: how do I assign directly to $arr given an unknown amount of keys (as an array)? Is it possible?

UPDATE:

Here's a pseudo code example of what I am trying to do:

// If this is supplied into function:
["key1","key2"]

// Then this is attempted to be returned:
$arr["key1"]["key2"];

I figured out how to do ^ that, but what I can't seem to figure out how to do this:

// If this is supplied for keys:
["key1","key2"] 

// And if this is supplied as value:
"test value"

// Then it should attempt to set:
$arr["key1"]["key2"] = "test value"

Is that possible?

Answer 1

You set the $nestedArrayValue reference to the array and in the loop you actually replace the entire array with the value $arr[$key]. It was necessary to change the reference to the next key:

$nestedArrayValue = &$arr;
foreach($keys as $key){
    // $nestedArrayValue = $arr[$key];
    $nestedArrayValue = &$nestedArrayValue[$key];
}

$nestedArrayValue = $value;

And it would also be good to check the key for existence:

$nestedArrayValue = &$arr;
$found = true;
foreach($keys as $key){
    if (array_key_exists($key, $nestedArrayValue)) {
        $nestedArrayValue = &$nestedArrayValue[$key];
    } else {
        $found = false;
        break;
    }
}

if ($found) {
    $nestedArrayValue = $value;
}