eigen/doc/snippets/TopicAliasing_block_correct.cpp

MatrixXi mat(3, 3);
mat << 1, 2, 3, 4, 5, 6, 7, 8, 9;
cout << "Here is the matrix mat:\n" << mat << endl;

// The eval() solves the aliasing problem
mat.bottomRightCorner(2, 2) = mat.topLeftCorner(2, 2).eval();
cout << "After the assignment, mat = \n" << mat << endl;