Rust does not prevent you from changing the model through iteration - it simply makes you explicitly think about it each time you are making changes. That is no

Rust does not prevent you from changing the model through iteration - it simply makes you explicitly think about it each time you are making changes. That is not against lean/agile way of working. I have worked on one of the largest Ruby monoliths around and I love Ruby, but I also appreciate that Rust can cut through some class of problems that you can't with Ruby (similarly it is much easier to bend Ruby to your will than Rust).