The tracking issue for this feature is: #44643

The splice() method on String allows you to replace a range of values in a string with another range of values.

A simple example:

#![allow(unused_variables)]
#![feature(splice)]
fn main() {
let mut s = String::from("α is alpha, β is beta");
let beta_offset = s.find('β').unwrap_or(s.len());

// Replace the range up until the β from the string
s.splice(..beta_offset, "Α is capital alpha; ");
assert_eq!(s, "Α is capital alpha; β is beta");
}