Lambda Expressions in C#

Lambda expression is a anonymous function that you can use to create delegates or expression tree types. These are useful for writing LINQ query expressions.

Expression Lambdas

A lambda expression with a statement on right side of => operator. These are used to construct expression trees. 

	class Program
	{
	delegate int Delegate1();
	delegate int Delegate2(int a);
	delegate int Delegate3(int a, int b);
	static void Main(string[] args)
	{
	//No parameters
	Delegate1 del1 = () => PrintValue();
	int val1 = del1(); //1
	//One parameter
	Delegate2 del2 = x => x * x;
	int val2 = del2(2); //4
	//Multiple parameters
	Delegate3 del3 = (x, y) => x * y;
	int val3 = del3(2, 3); //6
	}
	static int PrintValue()
	{
	return 1;
	}
	}

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Statement Lambdas

Resembles an expression lambda except that statements are enclosed in braces. 

	delegate string MyDelegate(string val);
	static void Main(string[] args)
	{
	MyDelegate del = n => {
	string s = n + "!!!";
	return s;
	};
	var delValue = del("Hello"); //Hello!!!
	}

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Async Lambdas

Incorporate asynchronous processing by using async and await keywords.

Generic Delegates ##

a delegate can define its own type parameters. A code that uses generic delegate can specify type argument to create a closed constructed type, just like when instantiating or creating a generic. 


What is a method group in C# (SO)

Lambdas with Standard Query Operators

Many standard query operators have an input parameter whose type is one of Func<T,TResult> family of generic delegates. 

Type inference in Lambdas

Usually you don't have to specify the type of input parameters because compiler can infer the type based on lambda body,  the parameters delegate type etc. 

Resources

Lambda Expressions (MSDN)
Lambda Expressions and Expression Trees Introduction (CodeProject)
Using Variance for Func and Action Generic Delegates