Why? String type has generally lots of choices for the values, so it prones to bugs. If your programing language supports strong-typing, you need to consider avoiding Strings as parameters of functions. Strong-typing led you Less bugs and validations. In Rust, it’s called a “newtype pattern”. The trinity, “Good naming (based on DDD) + good typing (struct) + enum”, helps us always. Newtype patterns in Rust https://doc.