refactor: Fix todo by using HashSet::difference (#505)

iroh/src/services.rs

@@ -5,6 +5,7 @@ use futures::StreamExt;
 use iroh_util::iroh_cache_path;
 use std::collections::HashSet;
 use std::io::{stdout, Write};
+use std::ops::Deref;
 use std::time::SystemTime;
 use sysinfo::PidExt;
 use tracing::info;
@@ -80,11 +81,9 @@ async fn start_services(api: &Api, services: HashSet<&str>) -> Result<()> {
  accum
  });
 
- // TODO (b5) - use services.difference here, but figure out how to
- // .collect() to &str instead of &&str
  let missing_services: HashSet<&str> = services
- .into_iter()
- .filter(|&service| missing_services.contains(service))
+ .difference(missing_services)
+ .map(Deref::deref)
  .collect();
 
  if missing_services.is_empty() {