What does this C# code with an "arrow" mean and how is it called?

Question

I was trying to enable SSL in my C# client program and found the following code in this answer:

System.Net.ServicePointManager.ServerCertificateValidationCallback +=     (se, cert, chain, sslerror) =>     {         return true;     }; 

I added the code to my program and it solved the problem, but I completely don't get how exactly it works.

The left part System.Net.ServicePointManager.ServerCertificateValidationCallback is some callback and += modifies that callback. But what does the remaining construct mean? I spent 20 minutes searching to at least find how it is properly called and where I can find more info on how to read that, but all in vain. I suppose it is somehow related to LINQ and searched for "LINQ arrow", but didn't find anything reasonable.

How is that (blah,blah,blah)=>{return true;} construct called and where can I find more info on such constructs?

Answer 1

That is a lambda expression. It is a very special anonymous delegate. Basically you are defining a method and not giving a name. Its parameters are to the left of the => and the method body is to the right of the =>. In your particular case,

(se, cert, chain, sslerror) => { return true; }; 

is an anonymous method defined by a lambda expression. This particular method has four parameters

object se X509Certificate cert X509Chain chain SslPolicyErrors sslerror 

and the method body is

return true; 

It's as if you had said

class ServerCertificateValidation {     public bool OnRemoteCertificateValidation(         object se,         X509Certificate cert,         X509Chain chain,         SslPolicyErrors sslerror     ) {         return true;     } } 

and then

var validation = new ServerCertificateValidation(); System.Net.ServicePointManager.ServerCertificateValidationCallback +=     validation.OnRemoteCertificateValidation; 

How is that (blah,blah,blah)=>{return true;} construct called and where can I find more info on such constructs?

It's called the same way that any other method is called. For example, you can do this:

Func<int, int, int> adder = (m, n) => m + n; 

Here I am defining a method that eats a pair of int and returns an int. That int is obtained by adding the values of the input parameters. It can be invoked like any other method.

int four = adder(2, 2);  

Here's an article on MSDN on lambda expressions and an article on the lambda operator. If you're really interested, the name comes from lambda calculus.