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All strings in python are immutable, as an example.
by TkTech 1y ago
All strings in python are immutable, as an example.
- masklinn 1y agoAlso JavaScript.
- fud101 1y agoJava too. Rust has only 99 string types, some of those are immutable also.
- masklinn 1y agoIt does not really matter in rust anyway: literals are &’static str so naturally immutable and essentially free, and mutable strings require jumping hoops to share, so it’s hard to unwittingly have one mutate from under you.
- steveklabnik 1y agoRust the language has one string type: &str The standard library also has String, CString, CStr, OsString, and OsStr. The latter four are for niche situations. 99.9% of the time, it's similar to Java: &str is Java's String, String is Java's StringBuffer/StringBuilder.
- ameliaquining 1y agoI would add Path and PathBuf to that list.
- steveklabnik 1y agoPaths are not strings, that's the whole point!
- simonask 1y agoWell... They're also not _not_ strings. In fact, what a perfect candidate for introducing a special type. :-)
- shikon7 1y agoThere is also &mut str. The nice thing about Rust is that the same memory area can be used as a "StringBuilder" with &mut str, and then as a "String" with &str. Once you have a &str reference, Rust statically guarantees that no one else cam mutate it.
- steveklabnik 1y agoYeah the type is really just str but I didn’t want to get into it. &mut str is kinda weird.
- simonask 1y agoYou can't really do anything useful with a `&mut str`. For example, you can't change the length of the string or any characters in the string (without unsafe code). The latter is perhaps surprising, but it's because strings in Rust are always UTF-8, so changing a logical character could imply changing the length of the string, and changing a byte could result in invalid UTF-8.
- whytevuhuni 1y agoYou're right, but just to add a bit more to this, you can call make_ascii_lowercase and make_ascii_uppercase on &mut str, which can sometimes be useful.
- fud101 1y ago99.9% of the time rust has 1 string type. The other 0.1% of the time it has 99, got it.
- steveklabnik 1y agoIt has two, not 99, with owned and borrowed pairs.
- ameliaquining 1y agoAll of those languages except JavaScript have mutable strings; they just have different names and API shapes. Python has io.StringIO, Java has StringBuilder, Rust has String. (JavaScript has less need for this because JavaScript strings are ropes in most widely used implementations, reducing the overhead of concatenation, though the language spec doesn't require this.)
- masklinn 1y agoBy your incredible criteria of things being mutable strings if they behave nothing like strings but can produce one, JavaScript absolutely does have a mutable string, it’s called Array. It’s also a mutable integer.
- ameliaquining 1y agoI don't consider JavaScript's Array to count because using it as a mutable string incurs a significant amount of additional overhead, because it has to box every character and check at runtime the type of each element. This is not true of the APIs that I listed.
- masklinn 1y agoAh yes, arbitrary and capricious goalposts moved randomly as you get unhappy with where your decisions lead. Truly a hallmark of solid thinking.
- echelon 1y agoRust has one core String type. String &str &mut str &'static str etc. These are just the language semantics. The other string types are non-Rust strings. Filesystem, C strings, etc. You only deal with them in dealing with specific OS and binding interfaces. 95% of the time you'll just be using String.