#include <iostream>
#include <sstream>

#define DEBUG 1
#define INFO 2
#define WARNING 3

/**
 * https://stackoverflow.com/questions/17595957/operator-overloading-in-c-for-logging-purposes
 */
class Logger {
private:
    /**
     * 引用类型必须使用：初始化列表来初始化
     */
    std::ostream& out_stream;

public:
    explicit Logger(int level, std::ostream& stream = std::cout) :
            out_stream(stream) {
        if (level == 1) {
            out_stream << "[DEBUG]";
        } else if (level == 2) {
            out_stream << "[INFO]";
        } else if (level == 3) {
            out_stream << "[WARNING]";
        }
    }

    ~Logger() {
        out_stream << std::endl;
    }

    template <typename T>
    Logger& operator<<(const T& data) {
        out_stream << data;
        return *this;
    }
};

#define LOG(level) Logger(level)

void test_log() {
    LOG(INFO) << "info";
    LOG(WARNING) << "warn";
}

int main(int argc, char** argv) {
    test_log();

    return 0;
}