#include <unistd.h>

#include <future>
#include <iostream>
#include <string>
#include <sstream>

template <typename T> class AsyncResult {
private:
    std::future<T> fut;
public:
#ifdef __BLOCKS__
    AsyncResult(BlockWrapper<T>&& bw) : fut(std::async(std::launch::async, bw)) {}
#else
    AsyncResult(std::function<T()>&& f) : fut(std::async(std::launch::async, f)) {}
#endif
    AsyncResult(AsyncResult&& r) : fut(std::move(r.fut)) {}
    operator T() { return fut.get(); }
    T operator+(T n);
};

#ifdef __BLOCKS__
#define LAMBDA(x) BlockWrapper<decltype(x)>(^{ return x; })
#else
#define LAMBDA(x) [=]()->decltype(x){ return x; }
#endif

#define ASYNC(x) AsyncResult<decltype(x)>(LAMBDA(x))

template <typename T> T AsyncResult<T>::operator+(T n) { return fut.get() + n; }
template <> std::string AsyncResult<std::string>::operator+(std::string n) {
    std::stringstream ss;
    ss << fut.get() << n;
    return ss.str();
}

std::string download(const std::string& url) {
    if (url == "BBB")
        sleep(20);
    else
        sleep(15);
    return url;
}

void process(const std::string& s) {
    std::cout << s << std::endl;
}

int main(void) {
    auto s1 = ASYNC(download("AAA"));
    auto s2 = ASYNC(download("BBB"));
    process(s1 + s2);
}