Working with Futures and Tasks

In asynchronous Rust, a Future is a trait that represents an asynchronous computation which may complete at some point. Think of it as a promise for a value that isn't ready yet.

• It's the core building block for async Rust.
• async fns in Rust actually return an anonymous type that implements the Future trait.
• The value isn't computed immediately; it's computed when the Future is "polled" by an executor.

A Future doesn't run on its own. An executor (like the Tokio runtime) repeatedly "polls" it to check if it has made progress or completed.

• When polled, a Future returns either Poll::Pending (not done yet) or Poll::Ready(T) (done, here's the result).
• If Pending, the executor knows to poll it again later when something relevant happens (e.g., I/O finishes).
• This polling mechanism is what allows many asynchronous operations to run concurrently on a single thread.