C# 4 and .NET 4

284 ❘ ChaPTer 11 lAnGuAGe inteGrAted Query
requires a string parameter and returns IEnumerable < Racer > , similar to the method that was implemented
before. For doing this, several generic Func < > delegates are defi ned, so you do not need to declare your
own delegate. A Lambda expression is assigned to the variable racersByCar . The left side of the Lambda
expression defi nes a car variable of the type that is the fi rst generic parameter of the Func delegate (a
string). The right side defi nes the LINQ query that uses the parameter with the where clause:
Func < string, IEnumerable < Racer > > racersByCar =
car = > from r in Formula1.GetChampions()
from c in r.Cars
where c == car
orderby r.LastName
select r;
Now you can use the Intersect() extension method to get all racers that won the championship with a
Ferrari and a McLaren:
Console.WriteLine("World champion with Ferrari and McLaren");
foreach (var racer in racersByCar("Ferrari").Intersect(
racersByCar("McLaren")))
{
Console.WriteLine(racer);
}
The result is just one racer, Niki Lauda:
World champion with Ferrari and McLaren
Niki Lauda
The Set operations compares the objects by invoking the GetHashCode() and
Equals() method of the entity class. For custom comparision, you can also pass an
object that implements the interface IEqualityComparer < T > . In the sample here,
the GetChampions() method always returns the same objects and thus the default
comparison works.
zip
The Zip() method is new with .NET 4 and enables you to merge two related sequences into one with a
predicate function.
First, two related sequences are created, both with the same fi ltering (country Italy) and ordering. For
merging this is important, as item 1 from the fi rst collection is merged with item 1 from the second
collection, item 2 with item 2, and so on. In case the count of the two sequences is different, Zip() just
stops when the end of the smaller collection is reached.
The items in the fi rst collection have a Name property and the items in the second collection have LastName
and Starts properties.
Using the Zip() method on the collection racerNames requires the second collection racerNamesAndStarts
as the fi rst parameter. The second parameter is of type Func < TFirst, TSecond, TResult > . This
parameter is implemented as a Lambda expression and receives the elements of the fi rst collection with the
parameter first , and the elements of the second collection with the parameter second . The implementation
creates and returns a string containing the Name property of the fi rst element and the Starts property of the
second element:
var racerNames = from r in Formula1.GetChampions()
where r.Country == "Italy"
orderby r.Wins descending
select new
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