Immutability is very very common. It makes reasoning much simpler. Source code control systems don't mutate in place. They create new versions. All modern rel

Immutability is very very common. It makes reasoning much simpler. Source code control systems don't mutate in place. They create new versions. All modern relational databases (Oracle, Sql Server, Postgres) don't modify records in place. They create new versions. All cloud based file systems (google docs) create new versions. When you have this mindset of 'any mutation needs to go into a different version, a new variable', it simplifies a whole lot of reasoning when things don't work as expected. Try it out.