Lambda Expressions in C# From Beginner To Expert - Jaliya Udagedara

Lambda Expressions in
C# From Beginner To
Expert
Jaliya Udagedara

What are we going to discuss today?
Introduction to Lambda Expressions
What are Delegates in C#
The Evolution of Delegates in C#
Demo 1 - Delegates and Named Methods, Anonymous Methods
Lambdas as Generic Delegates
Action
Func
Predicate
Lambdas as Callable Entities
Lambda Expression Execution
Lambdas as Callbacks
Demo 2 – Lambda Expressions

Introduction to Lambda Expressions
Introduced with .NET 3.5/C# 3.0
Supersede anonymous methods
Anonymous methods enable you to omit the parameter
list
Unnamed, inline functions
Used wherever delegates are required
(input parameters) => expression

Expression Lambdas
(input parameters) => expression
Statement Lambdas
(input parameters) => {statement;}
Async Lambdas
(input parameters) => async {statement;}

What are Delegates in C#
Delegates are like C++ function pointers
Makes it possible to treat methods as entities.
Assign to variables
Pass as parameters
Delegates can be chained together; for
example, multiple methods can be called on a
single event.Does delegates are exactly same as C++ function
pointers?
Does methods has to match the delegate type exactly?

What are Delegates in C# contd.
Delegates are like C++ function pointers but are
type safe.
Variance in Delegates
Covariance permits a method to have return type that is
More derived than that defined in the delegate
Contravariance permits a method that has parameter
types that are less derived than those in the delegate type.

The Evolution of Delegates in C#
C# 1.0 the only way to declare a delegate was to
use named methods.
C# 2.0 introduced anonymous methods as a way to
write unnamed inline statement blocks that can be
executed in a delegate invocation.
C# 3.0 introduced lambda expressions, which are
similar in concept to anonymous methods but more
expressive and concise.

Classic Delegate Example
btnHelloWorld.Click +=
new
EventHandler(btnHelloWorld_Click);

Anonymous Methods
btnHelloWorld.Click += delegate(System.Object
sender, System.EventArgs e) { … };
Lambda Expressions
btnHelloWorld.Click += (sender, e) => { ... };

Lambdas as Generic Delegates
Generic delegates were new in .NET 2.0
Action Delegates
Func Delegates
Predicate Delegates

Action Delegate
Zero, one or more input parameters, and does not
return anything.
Takes up to 16 parameters
Array.ForEach method and List.ForEach
Perform an action on each element of the array or
list
Action<int,int,string>

Func Delegate
Zero, one or more input parameters, and returns a
value
Takes up to 16 parameters
List.First
Func<int,int,string>

Predicate Delegate
Encapsulates a method that evaluates to True or
False
Takes one parameter
List.Find
Func<int>

Lambdas as Callable Entities
Lambda expressions can be assigned to a delegate
variable
Lambda expression is executed when the delegate
is executed
Func<int, string> myFunc = x =>
{
return String.Format("{0}*{0} is {1}", x, x * x);
};
Console.WriteLine(myFunc(4));

Lambda Expression Execution
Lambda expressions are executed when they are
called, not when they are constructed
Variable value used is the value at execution time

Example: Local Variables
int y = 0;
Func<int, string> myFunc = x => (x +
y).ToString();
y = 10;
Console.WriteLine(myFunc(5));
Answer?

Lambdas as Callbacks
Callback
“Executable code that is passed as an argument to other
code”
Passes a function to a function
static void DoWork()
{
CallBack(s => Console.WriteLine(s));
}
static void CallBack(Action<string> MyAction)
{
MyAction("Completed");
}

• Lambdas as Generic Delegates
• Lambdas as Callable Entities
• Lambdas as Callbacks

Thank You!
http://www.jaliyaudagedara.blogspot.com/

Lambda Expressions in C# From Beginner To Expert - Jaliya Udagedara

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