> Compare this with Java or Rust where you have separate types for mutable strings (StringBuilder in Java; String in Rust) and immutable strings (String in Java

> Compare this with Java or Rust where you have separate types for mutable strings (StringBuilder in Java; String in Rust) and immutable strings (String in Java; str in Rust). Not to detract from your point (which is broadly correct) but this isn't exactly right for Rust. Or at least isn't the right way to phrase it. Rust has one string type, `str`, which can be referenced immutably (`&str`) or mutably `&mut str`. What `str` can't do is manage memory, which means it can't grow a string. `String` is more correctly a `StringBuffer` (technically a `Vec<u8>` albeit with additional checks). It can manage memory and therefore grow the size of the string, either by using spare capacity or by reallocating the memory. It is not really a string type in itself; it's just a memory buffer for holding a `str`. This is all a long winded way of saying Rust separates managing memory from operating on the memory. This isn't the same as an mutable/immutable distinction although it is in some ways similar to growable/un-growable.