// PROJECT-EXAMPLE
T Echo<T>(T value) => value;
System.Console.WriteLine(Echo(7));
System.Console.WriteLine(Echo("ore"));

T FirstOrFallback<T>(IReadOnlyList<T> values, T fallback)
{
    return values.Count > 0 ? values[0] : fallback;
}

int first = FirstOrFallback(new[] { 10, 20 }, 0);
UO.Print(first.ToString());

sealed class Store<T> where T : notnull
{
    private readonly HashSet<T> values = new();
    public bool Add(T value) => values.Add(value);
    public int Count => values.Count;
}

var store = new Store<string>();
store.Add("self");
UO.Print(store.Count.ToString());