Marking method async

Context: Add the async modifier to any method that uses await. The method must return Task, Task<T>, ValueTask, ValueTask<T>, or void.

using System.Threading.Tasks;

public class Example
{
    public async Task DoWorkAsync()
    {
        await Task.Delay(100);
    }

    public async Task<int> GetNumberAsync()
    {
        await Task.Delay(100);
        return 42;
    }
}

Rules

• async methods can have await inside.
• The compiler transforms the method into a state machine.
• Parameter names cannot be await (unless escaped with @await).

Real-world usage example

Console application: Mark Main as async Task (C# 7.1+).

using System.Threading.Tasks;

class Program
{
    static async Task Main(string[] args)
    {
        await DownloadAsync();
    }

    static async Task DownloadAsync() => await Task.Delay(100);
}

Example: async Main in C#

Related sections

• 9.2 async and await
• 9.2.2 await unwraps the result