C# 5.0 Programmer's Reference

Extension Methods ❘ 751
An async lambda is a lambda expression with the async keyword added, so the program can execute
it asynchronously. For example, the following code adds an asynchronous statement lambda to the
countButton control’s Click event.
private void Form1_Load(object sender, EventArgs e)
{
countButton.Click += async (button, args) =>
{
for (int i = 0; i < 5; i++)
{
Console.WriteLine(i);
await System.Threading.Tasks.Task.Delay(1000);
}
};
}
Extension Methods
To make an extension method, place a static method in a static class. Add the keyword this
before the method’s first parameter and give that parameter the type that you want to extend. For
example, the following code defines a RemoveNonLetters string extension method.
public static class StringExtensions
{
public static string RemoveNonLetters(this string text)
{
string result = "";
foreach (char ch in text)
if (((ch >= 'a') && (ch = 'A') && (ch