Is there a method like JavaScript's substr in Rust?

Question

I looked at the Rust docs for String but I can't find a way to extract a substring.

Is there a method like JavaScript's substr in Rust? If not, how would you implement it?

str.substr(start[, length]) 

The closest is probably slice_unchecked but it uses byte offsets instead of character indexes and is marked unsafe.

Answer 1

For characters, you can use s.chars().skip(pos).take(len):

fn main() {     let s = "Hello, world!";     let ss: String = s.chars().skip(7).take(5).collect();     println!("{}", ss); } 

Beware of the definition of Unicode characters though.

For bytes, you can use the slice syntax:

fn main() {     let s = b"Hello, world!";     let ss = &s[7..12];     println!("{:?}", ss); } 

Answer 2

You can use the as_str method on the Chars iterator to get back a &str slice after you have stepped on the iterator. So to skip the first start chars, you can call

let s = "Some text to slice into"; let mut iter = s.chars(); iter.by_ref().nth(start); // eat up start values let slice = iter.as_str(); // get back a slice of the rest of the iterator 

Now if you also want to limit the length, you first need to figure out the byte-position of the length character:

let end_pos = slice.char_indices().nth(length).map(|(n, _)| n).unwrap_or(0); let substr = &slice[..end_pos]; 

This might feel a little roundabout, but Rust is not hiding anything from you that might take up CPU cycles. That said, I wonder why there's no crate yet that offers a substr method.