Comment by tialaramex
1 day ago
Rust apparently got relatively close to not having &str as a primitive type and instead only providing a library alias to &[u8] when Rust 1.0 shipped.
Score another for Rust's Safety Culture. It would be convenient to just have &str as an alias for &[u8] but if that mistake had been allowed all the safety checking that Rust now does centrally has to be owned by every single user forever. Instead of a few dozen checks overseen by experts there'd be myriad sprinkled across every project and always ready to bite you.
It wouldn't have been an alias, it would have been struct Str([u8]). Nothing would have been different about the safety story.
https://github.com/rust-lang/rfcs/issues/2692
I love this kind of historical knowledge. Thanks for sharing it!
Even so you end up with paper cuts like len which returns the number of bytes.
The problem with string length is there's probably at least four concepts that could conceivably be called length, and few people are happy when none of them are len.
Of the top of my head, in order of likely difficulty to calculate: byte length, number of code points, number of grapheme/characters, height/width to display.
Maybe it would be best for Str not to have len at all. It could have bytes, code_points, graphemes. And every use would be precise.
> The problem with string length is there's probably at least four concepts that could conceivably be called length.
The answer here isn't to throw up your hands, pick one, and other cases be damned. It's to expose them all and let the engineer choose. To not beat the dead horse of Rust, I'll point that Ruby gets this right too.
Similarly, each of those "views" lets you slice, index, etc. across those concepts naturally. Golang's string is the worst of them all. They're nominally UTF-8, but nothing actually enforces it. But really they're just buckets of bytes, unless you send them to APIs that silently require them to be UTF-8 and drop them on the floor or misbehave if they're not.
Height/width to display is font-dependent, so can't just be on a "string" but needs an object with additional context.
You could also have the number of code UNITS, which is the route C# took.
Problems arise when you try to take a slice of a string and end up picking an index (perhaps based on length) that would split a code point. String/str offers an abstraction over Unicode scalars (code points) via the chars iterator, but it all feels a bit messy to have the byte based abstraction more or less be the default.
FWIW the docs indicate that working with grapheme clusters will never end up in the standard library.
3 replies →
. (early morning brain fart -- I need my coffee)
So it's true that technically the primitive type is str, and indeed it's even possible to make a &mut str though it's quite rare that you'd want to mutably borrow the string slice.
However no &str is not "an alias for &&String" and I can't quite imagine how you'd think that. String doesn't exist in Rust's core, it's from alloc and thus wouldn't be available if you don't have an allocator.
str is not really a "primitive type", it only exists abstractly as an argument to type constructors - treating the & operator as a "type constructor" for that purpose, but including Box<>, Rc<>, Arc<> etc. So you can have Box<str> or Arc<str> in addition to &str or perhaps &mut str, but not really 'str' in isolation.