Question

I would like to have my comparison functions accessible by using a key. This is what I have tried. I think my problem is how I’m declaring the type for the dictionary value.

internal static int CompareUsersByEmail(MembershipUser a, MembershipUser b)
{
    // imagine null checking happening here.
    return string.Compare(a.Email, b.Email, true);
}

public static void Sort(List<MembershipUser> list, string expression) {

    // I can do this
    list.Sort(CompareUsersByEmail);

    // but not this
    Dictionary<string, Func<MembershipUser, MembershipUser, int>> compareFns;
    compareFns = new  Dictionary<string, Func<MembershipUser, MembershipUser, int>>();
    compareFns["Email"] = CompareUsersByEmail;
    list.Sort(compareFns[expression]); // where expression would be "Email"
}

Is this possible?

Answer 1

Change your dictionary type to:

Dictionary<string, Comparison<MembershipUser>> compareFns;

I believe it will then work with no other changes. The method group conversion to Comparison<MembershipUser> will still work, and now you can call List<T>.Sort(Comparison<T>).