Lambda Expressions in C#

(You should have a good understanding of Delegates, if you want to understand Lambda Expressions.)

What is a Lambda Expression:

Lambda Expressions are nothing but anonymous methods, using which you can create delegates and expression trees.(Expression trees needs will be explained in a separate article. )

If Lambda expressions are just anonymous methods why do we need them? What is the use of it?

Basically Lambda Expressions simplifies the anonymous methods syntactically. The whole code can be concise and neat. It takes another step ahead of Anonymous functions. So it is a good idea to read Anonymous Methods before before moving forward.

Look at the code below from last example.

int square = p.GenericCalculation(delegate(int x) { return x * x; }, 5);

The same thing can be again rewritten to

int square = p.GenericCalculation(x=>x*x, 5);

The delegate is replaced by x=>x*x. As you can see the syntax is much simplified. => is the Lambda operator. It is read 'goes to'. So the expression is read as 'x goes to x*x'. As you can see the right side got only one statement in the example. Whatever is the right side is evaluated to, would be the return type of the expression. If there are more than one statement then you may rewrite the expression as

int square = p.GenericCalculation(
                                    x=> { 
                                           int y= x*x; 
                                           if( y>0 ) 
                                           {
                                               return y;
                                           }
                                           else
                                           {
                                               return 1;
                                           } 
                                         }
                                     , 5);

When there are multiple statements in your Lambda Expression you should include the whole block in the curly brackets.And there should be explicit return statement if the lambda expression supposed to return anything. Please note that the method GenericCalculation expects a delegate which takes one integer parameter and expects a return type of integer. And that is the reason we are returning an integer in this example.

A lambda which takes no parameters would look like

()=> { 
           if( person.age > 18 )
           {
           }
           else
           {
           }    
        }

A lambda which takes 2 parameters would look like

(x,y)=> { 
           if( x > y )
           {
           }
           else
           {
           }    
        }

So our Delegates article code can be rewritten to as follows

class Program
    {
        static void Main(string[] args)
        {
            Program p = new Program();
            int square = p.GenericCalculation(x=>x*x, 5);
            Console.WriteLine("Square of 5 is {0}", square);
            int cube = p.GenericCalculation(x=>x*x*x, 5); 
            Console.WriteLine("Cube of 5 is {0}", cube);
            Console.ReadKey();
        }
        int GenericCalculation( Calc Generic, int x )
        {
            return Generic(x);
        }
    }

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