Rust Quick Start Guide

IndexMut

The IndexMut trait represents the abilities to assign to a contained value using the x[y] = z syntax. Like the Index trait, it lets us look up a contained data value by providing an index value, but it produces a mutable borrow of the contained value, which can be used to change it.

Implementing IndexMut looks like this:

pub struct IndexExample { first: u32, second: u32, third: u32, junk: u32,}impl<'a> IndexMut<&'a str> for IndexExample {    fn index_mut(&mut self, index: &'a str) -> &mut u32 {        match index {            "first" => &mut self.first,            "second" => &mut self.second,            "third" => &mut self.third,            _ => &mut self.junk,        }    }}

Notice that we've added a junk value to the IndexExample structure. We did that because there's no way to indicate that ...