Deep Merge Two Associative Arrays

<?php
function array_merge_recursive_distinct(array &array1, array &array2):
{
    $merged = $array1;
    foreach ($array2 as $key => &$value) {
        if (is_array($value) && isset($merged[$key]) && is_array($merged[$key])) {
            $merged[$key] = array_merge_recursive_distinct($merged[$key], $value);
        } else {
            $merged[$key] = $value;
        }
    }
    return $merged;
}

$defaultConfig = [
    'database' => [
        'host' => 'localhost',
        'port' => 3306,
        'user' => 'root'
    ],
    'cache' => [
        'enabled' => true,
        'driver' => 'file'
    ],
    'features' => ['comments', 'ratings']
];

$userConfig = [
    'database' => [
        'host' => 'remote_db',
        'password' => 'secret'
    ],
    'cache' => [
        'driver' => 'redis'
    ],
    'features' => ['ratings', 'analytics']
];

$finalConfig = array_merge_recursive_distinct($defaultConfig, $userConfig);
print_r($finalConfig);

/*
Output:
Array
(
    [database] => Array
        (
            [host] => remote_db
            [port] => 3306
            [user] => root
            [password] => secret
        )

    [cache] => Array
        (
            [enabled] => true
            [driver] => redis
        )

    [features] => Array
        (
            [0] => comments
            [1] => ratings
            [2] => analytics
        )

)

Note: The output for 'features' differs from initial thought. The custom merge function will append numeric keys for arrays like 'features'. If overwrite of numeric keys is desired, a more complex logic is needed. For typical config, string keys are usually merged this way. For a pure overwrite of 'features', you would assign $merged['features'] = $value directly instead of array_merge_recursive_distinct on it. The code provided does a deep merge where string keys are overwritten and numeric keys are appended if both are arrays, which is often the desired behavior for config arrays like 'features' that can be extended.
*/
?>