Async and Await

Boo supports the async/await pattern as implemented in C# 5.0.

Unlike C#, Boo does not implement async and await as keywords; instead it uses Boo's metaprogramming facilities. A method can be marked as asynchronous by adding the [AsyncAttribute] attribute to it, while marking a closure as async and awaiting a method call are done with metamethod invocations. (All three of these metaprogramming features are found in Boo.Lang.Extensions, which the compiler automatically references by default, so for all intents and purposes they can be considered built-in by Boo developers.)

Examples:

Async hello world:

import System.Threading
import System.Threading.Tasks

[async] def F(a as string) as Task:
	await Task.Factory.StartNew({ System.Console.WriteLine(a) })

F('Hello, World!').Wait()

Async closure:

import System.Threading
import System.Threading.Tasks
import System

def Foo(f as Func[of Task[of int]]):
    return f()

Console.WriteLine(TestCase.Foo(async({ return 14 })))

(Please note that these are examples of the syntax only, and not realistic uses of the feature.)

Credits: Both the feature implementation and the test suite were ported from Microsoft's official implementation in the Roslyn C# compiler by Mason Wheeler, with significant assistance from Microsoft's Jonathan Marolf and Neal Gafter.