sticky_extension.cpp

#include <iostream>
#include<bits/stdc++.h>
using namespace std;

template<class T>
struct sticky_streamer_t {
    std::ostream* os = nullptr;
    T x;
    int order;
    sticky_streamer_t()=default;
    sticky_streamer_t(sticky_streamer_t const&)=default;
    sticky_streamer_t(std::ostream* os, T&& x, int order = 1) : os(os), x(x), order(order) { }
    sticky_streamer_t(sticky_streamer_t&& ss) : os(ss.os), x(ss.x), order(ss.order) { ss.os = nullptr; }
    template<class U>
    sticky_streamer_t operator<<(U&& u) & {
        if (!os) return *this;
        if (order == 1) (*os) << forward<U>(u) << x;
        else            (*os) << x << forward<U>(u);
        return *this;
    }
    template<class U>
    sticky_streamer_t operator<<(U&& u) && {
        return std::move(*this << forward<U>(u));
    }
};

template<class T>
sticky_streamer_t<T> operator|(std::ostream& os, T&& x) {
    return {&os, forward<T>(x), 1};
}

template<class T>
sticky_streamer_t<T> operator|(T&& x, std::ostream& os) {
    return {&os, forward<T>(x), 2};
}

int main() {
    ('\n' | std::cout) << 1 << 2 << 3;
}