How to return a reference, when I really need it

From:

BlackLight <blacklight86@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Fri, 31 Jul 2009 05:27:30 -0700 (PDT)

Message-ID:

<2b75b844-4704-44f3-a186-8dc382293544@24g2000yqm.googlegroups.com>

Hi,

I'm actually developing a tiny C++ library for managing linear algebra
operations, but I have a problem in managing the reference to an
object as return value. This is the method I wrote:

Vector Matrix::operator[] (size_t i) throw() {
        if (i >= rows)
                throw InvalidMatrixIndexException();

        vector<float> row;

        for (int j=0; j < cols; j++)
                row.push_back(matrix[i][j]);

        return Vector(row);
}

where Matrix is a class I wrote for matrices management, and Vector is
another class (fundamentally a wrapping around vector<float> I wrote
for doing cool mathematical tricks, like sums, scalar products, norms
etc.). This is the actual implementation, but I would like to return a
reference to the Vector object, i.e. Vector& Matrix::operator[] (...).
I need it to do tricks like

Matrix A;
A[0][0] = 1.0;

or something like that, and this is not possible returning the Vector
object as a value. But if I declare a local Vector object and I return
its reference, I've got a problem as returning the reference of a
local variable. Has any of you a solution for this?

Thanks,
BlackLight