yiisoft/yii2 · error · InvalidArgumentException

Argument $array must be an array or implement Traversable

Error message

Argument $array must be an array or implement Traversable

What it means

Error "Argument $array must be an array or implement Traversable" thrown in yiisoft/yii2.

Source

Thrown at framework/helpers/BaseArrayHelper.php:1084

     * // [
     * //     'A.0' => 1
     * //     'A.1' => 2
     * //     'B.C' => 1
     * //     'B.D' => 2
     * //     'E' => 1
     * // ]
     * ```
     *
     * @param array $array the input array to be flattened in terms of name-value pairs.
     * @param string $separator the separator to use between keys. Defaults to '.'.
     *
     * @return array the flattened array.
     * @throws InvalidArgumentException if `$array` is neither traversable nor an array.
     */
    public static function flatten($array, $separator = '.'): array
    {
        if (!static::isTraversable($array)) {
            throw new InvalidArgumentException('Argument $array must be an array or implement Traversable');
        }

        $result = [];

        foreach ($array as $key => $value) {
            $newKey = $key;
            if (is_array($value)) {
                $flattenedArray = self::flatten($value, $separator);
                foreach ($flattenedArray as $subKey => $subValue) {
                    $result[$newKey . $separator . $subKey] = $subValue;
                }
            } else {
                $result[$newKey] = $value;
            }
        }

        return $result;
    }

View on GitHub (pinned to 66f00d18a2)

When it happens

Trigger: Thrown at framework/helpers/BaseArrayHelper.php:1084 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of yiisoft/yii2@66f00d18a2 (2026-08-17). Data as JSON: /api/errors/b592f77fe17e0c58. Report an issue: GitHub.