Lambda Expressions in C#.NET

Lambda Expressions

Lambda Expressions make things even easier by allowing you to avoid the anonymous method and that annoying statement block:

class Program
{
static void Main(string[] args)
{
List names = new List();
names.Add("Dave");
names.Add("John");
names.Add("Abe");
names.Add("Barney");
names.Add("Chuck");
string abe = names.Find((string name)

=> name.Equals("Abe"));
Console.WriteLine(abe);
}
}

Because Lambda Expressions are smart enough to infer variable types, I don't even have to explicity mention that name is a string above. I can remove it for even more simplicity and write it as such:

class Program
{
static void Main(string[] args)
{
List names = new List();
names.Add("Dave");
names.Add("John");
names.Add("Abe");
names.Add("Barney");
names.Add("Chuck");
string abe = names.Find(name =>

name.Equals("Abe"));
Console.WriteLine(abe);
}
}

Now there is no particular reason why I have to use name as my variable. Often developers will use 1 character variable names in Lambda Expressions just to keep things short. Here we replace name with p and all works the same.

class Program
{
static void Main(string[] args)
{
List names = new List();
names.Add("Dave");
names.Add("John");
names.Add("Abe");
names.Add("Barney");
names.Add("Chuck");
string abe = names.Find(p => p.Equals("Abe"));
Console.WriteLine(abe);
}
}

Lambda Expressions Using a Customer Class
I used a list of strings above, but you can just as easily use a list of objects to do the same thing. I will take an abbreviated form of a Customer Class:

public class Customer
{
public int Id;
public string Name;
public string City;
public Customer(int id, string name, string city)
{
Id = id;
Name = name;
City = city;
}
}

and now use Lambda Expressions to find a particular Customer with a name of "Abe".

class Program
{
static void Main(string[] args)
{
List customers = new List();
customers.Add(new Customer(1,"Dave","Sarasota"));
customers.Add(new Customer(2,"John","Tampa"));
customers.Add(new Customer(3,"Abe","Miami"));
Customer abe = customers.Find(c =>

c.Name.Equals("Abe"));
}
}

Again, we could make things more obvious by explicity saying that c is of type Customer, but I wouldn't bet on many people doing it :) You could write the above as follows:
class Program
{
static void Main(string[] args)
{
List customers = new List();
customers.Add(new Customer(1,"Dave","Sarasota"));
customers.Add(new Customer(2,"John","Tampa"));
customers.Add(new Customer(3,"Abe","Miami"));
Customer abe = customers.Find((Customer c) =>

c.Name.Equals("Abe"));
}
}

Combining Extension Methods and Lambda Expressions for Help In Finding Our Customer
Let's say we have a custom CustomerCollection Class not within our control that doesn't provide us an easy way to find a Customer:

public class CustomerCollection :

IEnumerable
{
IEnumerable _customers;
public CustomerCollection(IEnumerable

customers)
{
_customers = customers;
}
public IEnumerator GetEnumerator()
{
foreach (Customer customer in _customers)
yield return customer;
}
System.Collections.IEnumerator System.Collections

.IEnumerable.GetEnumerator()
{
return _customers.GetEnumerator();
}
}

Let's add an Extension Method to the CustomerCollection Class, called GetCustomer:

public static class CustomerExtensions
{
public static Customer GetCustomer(this

CustomerCollection customers,

Predicate isMatch)
{
foreach (Customer customer in customers)
if (isMatch(customer))
return customer;
return null;
}
}

And now, we can use the CustomerCollection Class to easily find Abe like:

class Program
{
static void Main(string[] args)
{
CustomerCollection collection = GetCustomers();
// Using my GetCustomer Method Extension...
Customer abe = collection.GetCustomer(c =>

c.Name.Equals("Abe"));
}

// Pretend We Don't See This :)
static CustomerCollection GetCustomers()
{
List customers = new List();
customers.Add(new Customer(1,"Dave","Sarasota"));
customers.Add(new Customer(2,"John","Tampa"));
customers.Add(new Customer(3,"Abe","Miami"));

return new CustomerCollection(customers);
}
}

This Is LINQ!But, of course, since CustomerCollection implements IEnumerable, in this case, IEnumerable, screw the Extension Methods and just use LINQ:

class Program
{
static void Main(string[] args)
{
CustomerCollection collection = GetCustomers();
// LINQ
var abe = collection.Single(c =>

c.Name.Equals("Abe"));
}

// Pretend We Don't See This :)
static CustomerCollection GetCustomers()
{
List customers = new List();
customers.Add(new Customer(1,"Dave","Sarasota"));
customers.Add(new Customer(2,"John","Tampa"));
customers.Add(new Customer(3,"Abe","Miami"));

return new CustomerCollection(customers);
}
}





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