Resource and scopes

Some rules for ownership in Rust:

• Each value in Rust has an owner.
• there can only be one owner at a time.
• When the owner goes out of scope, the value will be dropped

{
  let s = String::from("hello"); // allocates buffer on heap
  // do stuff with s
  print!("{}", s);
}                 // s out-of-scope, String buffer released

When a value is dropped, we can perform end-of-life actions before releasing memory.

fn baz(mutex: Mutex, ...) {
    let guard = mutex.lock();  // lock acquired at initialization
    // do stuff
} 
// mutex automatically unlocked when guard is dropped

This idiom is also called "resource-acquisition-is-initialization," though a better name is scoped-based resource management.