How to borrow mutable value? - rust

Question

I've been trying to separate all my Redis operations in a separate implementation, but I got this error when I passed the Redis reference to the implementation.
error[E0596]: cannot borrow `*self.redis_client` as mutable, as it is behind a `&` reference
--> src/main.rs:30:21
|
30 | let _: () = self.redis_client.set("key", "value").unwrap();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot borrow as mutable
Code:
use redis::{Commands};
use std::error::Error;
fn main() -> Result<(), Box<dyn Error>> {
let redis_client_uri = String::from("redis://127.0.0.1:6379");
let redis_client = redis::Client::open(redis_client_uri)?;
let mut redis = redis_client
.get_connection()
.expect("Failed to connect redis");
let batch = vec!["Sample value".to_string()];
CacheOperations::new(&redis, batch);
Ok(())
}
struct CacheOperations<'a> {
redis_client: &'a redis::Connection,
batch: Vec<String>,
}
impl<'a> CacheOperations<'a> {
fn new(redis_client: &'a redis::Connection, batch: Vec<String>) -> Self {
Self {
redis_client: &redis_client,
batch: batch,
}
}
fn insert_batch(self) {
let _: () = self.redis_client.set("key", "value").unwrap();
}
}

Answer 1

You just need to use the mut keyword to indicate that a reference or value is mutable. When you use it with a lifetime, the mut goes after the lifetime usage (Ex: &'abc mut x).
use redis::{Commands};
use std::error::Error;
fn main() -> Result<(), Box<dyn Error>> {
let redis_client_uri = String::from("redis://127.0.0.1:6379");
let redis_client = redis::Client::open(redis_client_uri)?;
let mut redis = redis_client
.get_connection()
.expect("Failed to connect redis");
let batch = vec!["Sample value".to_string()];
// Use a mutable reference when creating the CacheOperations
CacheOperations::new(&mut redis, batch);
Ok(())
}
struct CacheOperations<'a> {
// Store a mutable reference
redis_client: &'a mut redis::Connection,
batch: Vec<String>,
}
impl<'a> CacheOperations<'a> {
// We need to consume a mutable reference
fn new(redis_client: &'a mut redis::Connection, batch: Vec<String>) -> Self {
// No need to reference the reference, we can store it as-is
Self { redis_client, batch }
}
// While not required here, you can use mut self to state that self is mutable
// when a function consumes self as an owned value.
fn insert_batch(mut self) {
let _: () = self.redis_client.set("key", "value").unwrap();
}
}