This is a very great point that I’d like to highlight. The main problem with languages of today is shared mutable state. It’s the default in every major languag

This is a very great point that I’d like to highlight. The main problem with languages of today is shared mutable state. It’s the default in every major language, and it is the wrong default because of the inherent complexity it brings. You can avoid this complexity by killing either one of the adjectives: shared OR mutable. Immutability is generally pitched as the only way to solve this problem, and it is definitely a valid solution, though not the only one. The other dimension to cut off is sharing. If mutable data is not shared, its mutability also becomes mostly irrelevant. Rust and Swift both support immutability as well as unshareable references. In Rust’s case, it’s more like organized sharing that prevents simultaneous mutation. In Swift’s case, structs truly can only have one reference.