think\Model::readTransform PHP Method

    protected function readTransform($value, $type)
    {
        if (is_array($type)) {
            list($type, $param) = $type;
        } elseif (strpos($type, ':')) {
            list($type, $param) = explode(':', $type, 2);
        }
        switch ($type) {
            case 'integer':
                $value = (int) $value;
                break;
            case 'float':
                if (empty($param)) {
                    $value = (double) $value;
                } else {
                    $value = (double) number_format($value, $param);
                }
                break;
            case 'boolean':
                $value = (bool) $value;
                break;
            case 'timestamp':
                if (!is_null($value)) {
                    $format = !empty($param) ? $param : $this->dateFormat;
                    $value = date($format, $value);
                }
                break;
            case 'datetime':
                if (!is_null($value)) {
                    $format = !empty($param) ? $param : $this->dateFormat;
                    $value = date($format, strtotime($value));
                }
                break;
            case 'json':
                $value = json_decode($value, true);
                break;
            case 'array':
                $value = is_null($value) ? [] : json_decode($value, true);
                break;
            case 'object':
                $value = empty($value) ? new \stdClass() : json_decode($value);
                break;
            case 'serialize':
                $value = unserialize($value);
                break;
        }
        return $value;
    }