You can use "little parts of the language" in Rust too; the cleanest and most foundational part of Rust is pure value-based programming with no mutability or referencing at all, much like in a functional language (but with affine types!). Everything else is built quite cleanly on top of that foundation, even interior mutability which is often considered incredibly obscure. (It's called "interior" because the outer cell's identity doesn't really mutate, even though its content obviously does.)