A common question from Rust newbies is why String/str don't allow simple indexing, like this:
let foo = "foobar";
let x = foo[0];
The answer has always been that foo[0] is both ambiguous and dangerous given that str is a UTF-8 string: it could be a byte offset returning a char, a byte offset returning a u8, a codepoint index returning a char, etc., each having its own potential pitfalls of panicking or slowness.
For the same reason that foo[0] is not allowed, foo[m..n] and foo[..n] and similar such "sliced" indexing operations shouldn't be allowed.
(It's also a bit strange that both String and str impl these traits; since String is Deref<str>, shouldn't it only be needed on str?)
A common question from Rust newbies is why
String/strdon't allow simple indexing, like this:The answer has always been that
foo[0]is both ambiguous and dangerous given thatstris a UTF-8 string: it could be a byte offset returning a char, a byte offset returning a u8, a codepoint index returning a char, etc., each having its own potential pitfalls of panicking or slowness.For the same reason that
foo[0]is not allowed,foo[m..n]andfoo[..n]and similar such "sliced" indexing operations shouldn't be allowed.(It's also a bit strange that both
Stringandstrimpl these traits; sinceStringisDeref<str>, shouldn't it only be needed onstr?)