yii\helpers\BaseVarDumper::dumpInternal PHP Method

    private static function dumpInternal($var, $level)
    {
        switch (gettype($var)) {
            case 'boolean':
                self::$_output .= $var ? 'true' : 'false';
                break;
            case 'integer':
                self::$_output .= "{$var}";
                break;
            case 'double':
                self::$_output .= "{$var}";
                break;
            case 'string':
                self::$_output .= "'" . addslashes($var) . "'";
                break;
            case 'resource':
                self::$_output .= '{resource}';
                break;
            case 'NULL':
                self::$_output .= 'null';
                break;
            case 'unknown type':
                self::$_output .= '{unknown}';
                break;
            case 'array':
                if (self::$_depth <= $level) {
                    self::$_output .= '[...]';
                } elseif (empty($var)) {
                    self::$_output .= '[]';
                } else {
                    $keys = array_keys($var);
                    $spaces = str_repeat(' ', $level * 4);
                    self::$_output .= '[';
                    foreach ($keys as $key) {
                        self::$_output .= "\n" . $spaces . '    ';
                        self::dumpInternal($key, 0);
                        self::$_output .= ' => ';
                        self::dumpInternal($var[$key], $level + 1);
                    }
                    self::$_output .= "\n" . $spaces . ']';
                }
                break;
            case 'object':
                if (($id = array_search($var, self::$_objects, true)) !== false) {
                    self::$_output .= get_class($var) . '#' . ($id + 1) . '(...)';
                } elseif (self::$_depth <= $level) {
                    self::$_output .= get_class($var) . '(...)';
                } else {
                    $id = array_push(self::$_objects, $var);
                    $className = get_class($var);
                    $spaces = str_repeat(' ', $level * 4);
                    self::$_output .= "{$className}#{$id}\n" . $spaces . '(';
                    if ('__PHP_Incomplete_Class' !== get_class($var) && method_exists($var, '__debugInfo')) {
                        $dumpValues = $var->__debugInfo();
                        if (!is_array($dumpValues)) {
                            throw new InvalidValueException('__debuginfo() must return an array');
                        }
                    } else {
                        $dumpValues = (array) $var;
                    }
                    foreach ($dumpValues as $key => $value) {
                        $keyDisplay = strtr(trim($key), "", ':');
                        self::$_output .= "\n" . $spaces . "    [{$keyDisplay}] => ";
                        self::dumpInternal($value, $level + 1);
                    }
                    self::$_output .= "\n" . $spaces . ')';
                }
                break;
        }
    }