How to initialize a static readonly variable using an anonymous method?

Question

I'm trying to clean up my code for initializing static readonly variables.

Original:

public static readonly List<int> MyList;

//Initialize MyList in the static constructor
static MyObject() { ... }

---

I decided to clean it up because CodeAnalysis said I should not use the static constructor (CA1810).

Cleanup:

public static readonly List<int> MyList = GetMyList();

//Returns the list
private static List<int> GetMyList() { ... }

---

I didn't really like the additional method, so I figured I'd try to get it to be all inline, but it won't work. I'm not sure what I'm doing wrong here...

public static readonly List<int> MyList =
    () =>
       {
           ...

           return list;
       };

I attempted to take the code within the GetMyList() method and place it in an anonymous delegate to return the list to assign, but it says I'm attempting to convert a delegate into a List<int>?

Answer 1

This looks a little weird, but try this:

public static readonly List<int> MyList = new Func<List<int>>(
() =>
{
    // Create your list here
    return new List<int>();
})();

The trick is creating a new Func<List<int>> and invoking it.

Answer 2

The reason is that when you write

() =>
   {
       ...

       return list;
   };

You're actually declaring a delegate - a function that returns List<int>, but you're not actually invoking that function, and therefore this evaluates to Func<List<int>> and not to List<int>.

I'm not quite sure why you're trying to remove your static constructor though. Static constructors have their uses, and in some cases even make the code cleaner and more readable.