SWAG

    auto sw1 = make_swag(plus<ll>(), 0LL);
    auto sw = make_swag(multiplies<MyMatrix>(), MyMatrix{{1,0},{0,1}});
              // operator and its unit element.
              // operator should be associative.
    sw.push(obj1);   // push obj1 into the queue
    sw.pop();        // pop the front element
    T v = sw.get_val(); // calculate the aggregated value e1 `op` e2 `op` ... `op` en
                        //     where e1 is the front and en is the back
    T a = sw.front();   // the front element
    T b = sw.back();    // the back element
    auto vec = sw.vec_view();  // list the elements for debugging