Dictionary<TKey, TValue> constructor microbenchmark

Program.cs

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Diagnostics;

public class Program
{
    public static void Main()
    {
        const int iterations = 1000000;

        int[] sizes = new[] { 0, 1, 2, 3, 4, 5, 10, 25, 50, 100 };

        Measure(iterations, sizes, i => new object(), i => new object());
        Measure(iterations, sizes, i => i.ToString(), i => i.ToString());
        Measure(iterations, sizes, i => (long)i, i => (long)i);
        Measure(iterations, sizes, i => i, i => i);
    }

    private static void Measure<TKey, TValue>(int iterations, int[] sizes, Func<int, TKey> keySelector, Func<int, TValue> valueSelector)
    {
        foreach (int size in sizes)
        {
            Measure("Dictionary", iterations, size, keySelector, valueSelector, d => d);
        }

        foreach (int size in sizes)
        {
            Measure("DictionarySubclass", iterations, size, keySelector, valueSelector, d => new DictionarySubclass<TKey, TValue>(d));
        }

        foreach (int size in sizes)
        {
            Measure("ReadOnlyDictionary", iterations, size, keySelector, valueSelector, d => new ReadOnlyDictionary<TKey, TValue>(d));
        }
    }

    private static void Measure<TKey, TValue>(string name, int iterations, int size, Func<int, TKey> keySelector, Func<int, TValue> valueSelector, Func<Dictionary<TKey, TValue>, IDictionary<TKey, TValue>> factory)
    {
        IDictionary<TKey, TValue> dictionary = CreateDictionary(size, keySelector, valueSelector, factory);

        Console.Write("\"{0}<{1},{2}>\",", name, typeof(TKey).Name, typeof(TValue).Name);
        Console.Write("{0},", size);

        TimeSpan elapsed = Measure(dictionary, iterations, d => new Dictionary<TKey, TValue>(d));
        Console.Write(elapsed.TotalMilliseconds);

        Console.WriteLine();
    }

    private static IDictionary<TKey, TValue> CreateDictionary<TKey, TValue>(int size, Func<int, TKey> keySelector, Func<int, TValue> valueSelector, Func<Dictionary<TKey, TValue>, IDictionary<TKey, TValue>> factory)
    {
        var dictionary = new Dictionary<TKey, TValue>();

        if (size > 0)
        {
            for (int i = 0; i < size; i++)
            {
                dictionary.Add(keySelector(i), valueSelector(i));
            }
        }

        return factory(dictionary);
    }

    private static TimeSpan Measure<TKey, TValue>(IDictionary<TKey, TValue> dictionary, int iterations, Action<IDictionary<TKey, TValue>> action)
    {
        // Prime
        action(dictionary);

        // Clean up
        GC.Collect();
        GC.WaitForPendingFinalizers();
        GC.Collect();

        var sw = new Stopwatch();
        sw.Start();
        for (int i = 0; i < iterations; i++)
        {
            action(dictionary);
        }
        sw.Stop();

        return sw.Elapsed;
    }
}

public class DictionarySubclass<TKey, TValue> : Dictionary<TKey, TValue>
{
    public DictionarySubclass(Dictionary<TKey, TValue> dictionary)
    {
        foreach (var pair in dictionary) Add(pair.Key, pair.Value);
    }
}