Issue when using only a getter and issue with List in c#

Question

I'm working on an application that uses a list to handle previous guesses from the user. Below is the (private) list and the property for accessing the list.

To prevent privacy leak i'm using a ReadOnlyCollection, which is also the reason for me only having a getter in the property (elements are added inside the class directly to the list, not through the property).

Now to the problem. The code below generates to error message:

1. TheNameOfTheClass.PreviousGuesses.get must declare a body because it is not marked abstract or extern. Automatically implemented properties must define both get and set accessors.
2. Cannot implicity convert type 'System.Collections.Generic.List' to 'System.Collections.ObjectModel.ReadOnlyCollection.

How can this be solved? Thanks in advance!

private List<int> _previousGuesses;

public ReadOnlyCollection<int> PreviousGuesses {
    get {
        return _previousGuesses;
    }
}

EDIT: Ok, so problem nr 2 is solved (thanks Zortkun!). What about the first problem, that I can't use only a getter, any ideas?

Answer 1

I guess the favor is not to post the first thing that pops up on google but how about this?

   return _previousGuesses.AsReadOnly();

From here