Eigen library: Return expression instead of the vector itself

Is it possible to return some kind of expression, which then can be further used and simplified, instead of a vector itself?

I have a function Vector3<T> f(Vector3<T> const&, Vector3<T> const&); and I apply it in an expression of the form g = f(a1, b1).cwiseProduct(t1) + f(a2, b2).cwiseProduct(t2). I wonder if this can be optimized. It seems to be unnecessary that a vector is created when f returns. It might be more efficient to return an "expression" instead which then can be optimized for the evaluation of g.

Writing up my comment as it might be clearer as an answer. If you return auto rather than Vector3<T> then the expression type is retained.

E.g.

template <typename T>
auto f(Vector3<T> const& x, Vector3<T> const& y)
{
    return x + y;
}

template <typename T>
auto use_f(Vector3<T> const& a1, Vector3<T> const& b1, Vector3<T> const& t1,
           Vector3<T> const& a2, Vector3<T> const& b2, Vector3<T> const& t2)
{
    auto f1 = f(a1, b1);
    auto f2 = f(a2, b2);
    auto g = f1.cwiseProduct(t1) + f1.cwiseProduct(t2);
    return g;
}

Types of f1 & f2:

Eigen::CwiseBinaryOp<Eigen::internal::scalar_sum_op<double,double>,Eigen::Matrix<double,3,1,0,3,1>const,Eigen::Matrix<double,3,1,0,3,1>const>
Eigen::CwiseBinaryOp<Eigen::internal::scalar_sum_op<double,double>,Eigen::Matrix<double,3,1,0,3,1>const,Eigen::Matrix<double,3,1,0,3,1>const>

(this on Visual C++, might be a little different on gcc/clang)

Thanks to @Homer512, it should be noted that this approach is risky, in that if temporary objects are created in f, the use of auto will effectively return a pointer to a local variable in f, with the local variable going out of scope. In the docs, under "C++11 and the auto keyword", the problematic example given is

auto z = ((x+y).eval()).transpose();
// use or return z

problem is that eval() returns a temporary object which is then referenced by the Transpose<> expression. However, this temporary is deleted right after the first line.

The docs further note that the issue can be fixed by calling eval() on the whole expression; however this is equivalent in our case to returning the Vector3<T>, which is what we were trying to avoid.