Eigen vector constructor initialization vs comma initialization

Question

For Eigen vectors of a fixed size (eg Eigen::Vector3d, Eigen::Vector4f) there is the option to initialize the vector using the constructor as follows:

Eigen::Vector3d a(0.0, 1.0, 2.0);

However, Eigen also offers a way to use comma initialization of a general Eigen matrix that can be used in this case:

Eigen::Vector3d b;
b << 0.0, 1.0, 2.0;

Is one of the two methods preferable for speed or some other reasons? Or are they equal?

Answer 1

One advantage of the first version is that it will fail at compile time if you pass the wrong number of arguments, e.g. because you misstyped Vector2d as Vector3d.

Performance-wise, the compiler is able to optimize both the same. Checked it with GCC.