Methods ready and result of Future in Scala cannot be called directly

Question

I noticed that methods ready and result of scala.concurrent.Future cannot be invoked directly. When I call them in REPL I get an error. Thus I have to call Await.ready and Await.result instead.

It is Ok but looks a bit awkward. So now I wonder:

• why they cannot be invoked directly;
• why they are exposed as public API in that case.

Answer 1

The reasons are laid out in official doc:

The Future trait implements the Awaitable trait with methods method ready() and result(). These methods cannot be called directly by the clients– they can only be called by the execution context.

That way library designers enforce you to use those methods in proper environment (execution context, perhaps third party, or via Awaitable object to denote blocking operations explicitly).