a.rb

   Compiling cache-server v0.1.0 (file:///Users/stuart/coding/cLRUd/cache-server)
error[E0277]: the trait bound `std::rc::Rc<std::cell::RefCell<lru_cache::list::Node<std::string::String>>>: std::marker::Send` is not satisfied
  --> src/main.rs:24:12
   |
24 |     server.serve(|| Ok(
   |            ^^^^^ the trait `std::marker::Send` is not implemented for `std::rc::Rc<std::cell::RefCell<lru_cache::list::Node<std::string::String>>>`
   |
   = note: `std::rc::Rc<std::cell::RefCell<lru_cache::list::Node<std::string::String>>>` cannot be sent between threads safely
   = note: required because of the requirements on the impl of `std::marker::Send` for `std::collections::hash::table::RawTable<std::string::String, std::rc::Rc<std::cell::RefCell<lru_cache::list::Node<std::string::String>>>>`
   = note: required because it appears within the type `std::collections::HashMap<std::string::String, std::rc::Rc<std::cell::RefCell<lru_cache::list::Node<std::string::String>>>>`
   = note: required because it appears within the type `lru_cache::cache::LruCache<std::string::String>`
   = note: required because of the requirements on the impl of `std::marker::Send` for `std::sync::Mutex<lru_cache::cache::LruCache<std::string::String>>`
   = note: required because of the requirements on the impl of `std::marker::Sync` for `std::sync::Arc<std::sync::Mutex<lru_cache::cache::LruCache<std::string::String>>>`
   = note: required because of the requirements on the impl of `std::marker::Send` for `&std::sync::Arc<std::sync::Mutex<lru_cache::cache::LruCache<std::string::String>>>`
   = note: required because it appears within the type `[closure@src/main.rs:24:18: 27:11 cache:&std::sync::Arc<std::sync::Mutex<lru_cache::cache::LruCache<std::string::String>>>]`

error: aborting due to previous error

error: Could not compile `cache-server`.