Question

I would like to write a C# extension for generic Array but it’s always casting an Error. Here is the code i used to create extendsion for string[] which works well :

public static string[] Add(this string[] list, string s, bool checkUnique = false, bool checkNull = true){
    if (checkNull && string.IsNullOrEmpty(s)) return list;
    if (checkUnique && list.IndexOf(s) != -1) return list;

    ArrayList arr = new ArrayList();
    arr.AddRange(list);
    arr.Add(s);

    return (string[])arr.ToArray(typeof(string));
}

What i really want is do it more generic so it will also works for other types not only string (so i tried to replace all string specifics with generics T) :

public static T[] Add(this T[] list, T item, bool checkUnique = false){
    if (checkUnique && list.IndexOf(item) != -1) return list;

    ArrayList arr = new ArrayList();
    arr.AddRange(list);
    arr.Add(item);

    return (T[])arr.ToArray(typeof(T));
}

but the code won’t compile. It’s casting an error “error CS0246: The type or namespace name `T’ could not be found. Are you missing a using directive or an assembly reference?”

I already tried another solution around :

public static void AddIfNotExists<T>(this ICollection<T> coll, T item) {
     if (!coll.Contains(item))
         coll.Add(item);
 }

but it’s casting another error “error CS0308: The non-generic type `System.Collections.ICollection’ cannot be used with the type arguments”

As a side note, I’m using Unity C# (which is compiles against 3.5 I think). Can anyone help me ?

Answer 1

Your last method does not compile because of the missing reference to the System.Collections.Generic namespace. You seem to have included the reference to System.Collections only.