using System;
using System.Collections;
using System.Collections.Generic;

class Program {
    // *** before: ***
    // a collection stored object, so every element had to be cast back and
    // a wrong element was caught only at run time
    static int SumOld(ArrayList numbers) {
        int total = 0;
        foreach (object o in numbers)
            total += (int)o;              // unboxing on every element
        return total;
    }

    // *** in version 2.0: ***
    // List<T> keeps the type of the element, so the compiler checks it
    static int SumNew(List<int> numbers) {
        int total = 0;
        foreach (int n in numbers)        // no cast, no boxing
            total += n;
        return total;
    }

    // our own methods and classes take type parameters too
    static T Largest<T>(T a, T b) where T : IComparable<T> {
        return a.CompareTo(b) >= 0 ? a : b;
    }

    static void Main() {
        ArrayList old = new ArrayList();
        old.Add(1); old.Add(2); old.Add(3);
        old.Add("four");                  // compiles, and SumOld breaks on it
        Console.WriteLine(old.Count);

        List<int> fresh = new List<int>();
        fresh.Add(1); fresh.Add(2); fresh.Add(3);
        // fresh.Add("four");             // would not compile
        Console.WriteLine(SumNew(fresh));

        Dictionary<string, int> ages = new Dictionary<string, int>();
        ages["Ann"] = 31;
        Console.WriteLine(ages["Ann"]);
        Console.WriteLine(Largest(6, 7));
    }
}