Lambda Expression

Anatomy of the Lambda Expression

C# 3.0(.NET 3.5) introduced the lambda expression along with LINQ. The lambda expression is a shorter way of representing anonymous methods using some special syntax.

Reference - http://www.tutorialsteacher.com/linq/linq-lambda-expression

For example, following anonymous method checks if student is teenager or not:

Anonymous method in C#:

    
delegate(Student s) { return s.Age > 12 && s.Age < 20; };
        

Anonymous method in VB.Net:

    
Dim isStudentTeenAger = Function(s As Student) As Boolean
                                    Return s.Age > 12 And s.Age < 20
                        End Function
        

The above anonymous method can be represented using a Lambda Expression in C# and VB.Net as below:

Lambda Expression in C#:

s => s.Age > 12 && s.Age < 20

Lambda Expression in VB.Net:

Function(s) s.Age  > 12 And s.Age < 20

Let's see how the lambda expression evolved from the following anonymous method.

Anonymous method in C#:

delegate(Student s) { return s.Age > 12 && s.Age < 20; };

The Lambda expression evolves from anonymous method by first removing the delegate keyword and parameter type and adding a lambda operator:

Lambda Expression from Anonymous Method

The above lambda expression is absolutely valid, but we don't need the curly braces, return and semicolon if we have only one statement that returns a value. So we can eliminate it.

Also, we can remove parenthesis (), if we have only one parameter.

Lambda Expression from Anonymous Method

Thus, we got the lambda expression: s => s.Age > 12 && s.Age < 20 where s is a parameter,=> is the lambda operator and s.Age > 12 && s.Age < 20 is the body expression:

Lambda Expression Structure in C#

Same way we got lambda expression in VB.Net can be written as below:

Lambda Expression Structure in VB.Net

Note :VB.Net doesn't support lambda operator =>

Lambda Expression with Multiple parameters:

You can wrap the parameters in parenthesis if you need to pass more than one parameter, as below:

Example: Specify multiple parameters in lambda expression C#

            
(s, youngAge) => s.Age >= youngage;

You can also give type of each parameters if parameters are confusing:

Example: Specify parameter type in lambda expression C#

            
(Student s,int youngAge) => s.Age >= youngage;

Example: Specify multiple parameters in lambda expression VB.Net

            
Function(s, youngAge) s.Age >= youngAge 

Lambd expression without any parameter:

It is not necessary to have atleast one parameter in a lambda expression. The lambda expression can be specify without any parameter also.

Example: Lambda expression with zero parameter.

            
() => Console.WriteLine("Parameter less lambda expression")

Multiple statements in body expression:

You can wrap expressions in curly braces if you want to have more than one statement in the body:

Example: Lambda expression C#

(s, youngAge) =>
{
  Console.WriteLine("Lambda expression with multiple statements in the body");
    
  Return s.Age >= youngAge;
}

Example: Lambda expression VB.Net

Function(s , youngAge)
    
    Console.WriteLine("Lambda expression with multiple statements in the body")
    Return s.Age >= youngAge

End Function 

Local variable in Lambda Expression body:

You can declare a variable in the expression body to use it anywhere in the expression body, as below:

Example: Lambda expression C#

s =>
{
   int youngAge = 18;

    Console.WriteLine("Lambda expression with multiple statements in the body");

    return s.Age >= youngAge;
}

Example: Lambda expression VB.Net

 Function(s) 
                                      
        Dim youngAge As Integer = 18
            
        Console.WriteLine("Lambda expression with multiple statements in the body")
            
        Return s.Age >= youngAge
            
End Function

You can invoke lambda expression as you invoke delegates. Learn how to invoke lambda expression in the next section.

Points to Remember:

1. Lambda Expression is a shorter way of representing anonymous method.
2. Lambda Expression syntax: parameters => body expression
3. Lambda Expression can have zero parameter.
4. Lambda Expression can have multiple parameters in parenthesis ().
5. Lambda Expression can have multiple statements in body expression in curly brackets {}.