C# 4 and .NET 4

lists ❘ 231
{
if (action == null) throw new ArgumentNullException("action");
}
foreach (T item in items)
{
action(item);
}
}
//...
For passing a method with ForEach , Action < T > is declared as a delegate that defi nes a method with a void
return type and parameter T:
public delegate void Action < T > (T obj);
With a list of Racer items, the handler for the ForEach() method must be declared with a Racer object as
parameter and a void return type:
public void ActionHandler(Racer obj);
Because one overload of the Console.WriteLine() method accepts Object as parameter, you can pass
the address of this method to the ForEach() method, and every racer of the collection is written to the
console:
racers.ForEach(Console.WriteLine);
You can also write a Lambda expression that accepts a Racer object as parameter and does the Console.
WriteLine() with the implementation. Here, the format A is used with the ToString() method of the
IFormattable interface to display all information about the racer:
racers.ForEach(r = > Console.WriteLine("{0:A}", r));
Lambda expressions are explained in Chapter 8, “ Delegates, Lambdas, and Events.”
removing elements
You can remove elements by index or pass the item that should be removed. Here, the fourth element is
removed by passing 3 to RemoveAt() :
racers.RemoveAt(3);
You can also directly pass a Racer object to the Remove() method to remove this element. Removing
by index is faster, because here the collection must be searched for the item to remove. The Remove()
method fi rst searches in the collection to get the index of the item with the IndexOf() method, and
then uses the index to remove the item. IndexOf() fi rst checks if the item type implements the interface
IEquatable < T > . If it does, the Equals() method of this interface is invoked to fi nd the item in the
collection that is the same as the one passed to the method. If this interface is not implemented,
the Equals() method of the Object class is used to compare the items. The default implementation
of the Equals() method in the Object class does a bitwise compare with value types, but compares
only references with reference types.
Chapter 7, “ Operators and Casts, ” explains how you can override the Equals()
method.
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