Append column to matrix, using Eigen library

It's quite a simple task, but I was not able to find an answer to it: Using the Eigen library, suppose I have `Matrix2Xd mat` and `Vector2d vec`, where ``` mat = 1 1 1 1 1 1 vec = 2 2 ``` Now I need something like `mat.addCol(vec)` such that afterwards ``` mat = 1 1 1 2 1 1 1 2 ``` What is the best (simplest) way to accomplish this? Please note, that this is not a duplicate of How do you make a matrix out of vectors in eigen?. I don't want to initialy construct the matrix but append to an existing one. Or is there maybe a trick, how to use the comma initialization in this case? The following code will fail: ``` Matrix2Xd mat(2,3); Vector2d vec; mat << 1, 1, 1, 1, 1, 1; vec << 2, 2; cout << mat << endl; mat << vec; // <-- crashes here cout << mat << endl; ``` Edit: The following works, but I don't like the need of a temporary variable for such a basic task. Is there a better way? ``` Matrix2Xd tmp(2, mat.cols()+1); tmp << mat, vec; mat = tmp; ```