Go语言匿名函数返回值如何正确传递到外部函数？

func (client *ClientLoginModel) register() error {
    if len(client.ID) == 0 {
        log.InfoW("client register", "clientModel", client)
        client.GetInfo()

        var err error // 声明一个变量存储错误

        api.RegisterClient(*client, func(json *ResponseJson) {
            err = mapstructure.Decode(json.Data, client) // 将错误赋值给 err
            if err != nil {
                log.ErrorW("client info parse error", "err", err)
                return
            } else {
                log.InfoW("client register success", "id", client.ID)
                log.InfoW("write config")

                configMaps := make(map[string]interface{})
                configMaps["id"] = client.ID
                configMaps["userID"] = client.UserID

                err = base.SetConfigs(configMaps) // 将错误赋值给 err
                if err != nil {
                    log.ErrorW("write config error", "err", err)
                    return
                }
            }
        }, func(json *ResponseJson) {
            // 失败
            log.ErrorW("client register error", "err", json)
            return
        })

        return err // 返回存储的错误
    }
    return nil
}