duckTyping.cpp

#include <chrono>
#include <iostream>


auto start = std::chrono::steady_clock::now();

void writeElapsedTime()
{
    auto now = std::chrono::steady_clock::now();
    std::chrono::duration<double> diff = now - start;
    std::cerr << diff.count() << " sec, elapsed: ";
}


struct MessageSeverty{
    void writeMessage() const
    {
        std::cerr << "unexpected" << '\n';
    }
};


struct MessageInformation
{
    void writeMessage() const{
        std::cerr << "information" << '\n';
    }
};

struct MessageWarning{
    void writeMessage() const{
        std::cerr << "warning" << '\n';
    }
};


struct MessageFatal:MessageSeverty{};

template<typename T>
void writeMessage(T& messServer)
{
    writeElapsedTime();
    messServer.writeMessage();
}

int main()
{
    std::cout << '\n';

    MessageInformation messInfo;
    writeMessage(messInfo);

    MessageWarning messWarn;
    writeMessage(messWarn);

    MessageFatal messFatal;
    writeMessage(messFatal);

    std::cout << '\n';

    return 0;
}