What does SomeMethod(() => x.Something) mean in C#

Question

(Note the code is an example)

I have the following syntax:

SomeMethod(() => x.Something) 

What do the first brackets mean in the expression?

I'm also curious how you can get the property name from argument that is being passed in. Is this posssible?

Answer 1

What do the first brackets mean in the expression?

It's the lambda syntax for a method that takes no parameters. If it took 1 parameter, it'd be:

SomeMethod(x => x.Something);

If it took n + 1 arguments, then it'd be:

SomeMethod((x, y, ...) => x.Something);

I'm also curious how you can get the property name from argument that is being passed in. Is this possible?

If your SomeMethod takes an Expression<Func<T>>, then yes:

void SomeMethod<T>(Expression<Func<T>> e) {
    MemberExpression op = (MemberExpression)e.Body;
    Console.WriteLine(op.Member.Name);
}

Answer 2

The () is an empty argument list. You're defining an anonymous function that takes no arguments and returns x.Something.

Edit: It differs from x => x.Something in that the latter requires an argument and Something is called on that argument. With the former version x has to exist somewhere outside the function and Something is called on that outside x. With the latter version there does not have to be an outside x and even if there is, Something is still called on the argument to the function and nothing else.