DynamicObejct.cs

using System;
using System.Collections.Generic;
using System.Dynamic;
using System.Linq.Expressions;

// The class derived from DynamicObject.
public class DynamicDictionary : DynamicObject
{
    // The inner dictionary.
    Dictionary<string, object> dictionary
        = new Dictionary<string, object>();

    // This property returns the number of elements
    // in the inner dictionary.
    public int Count
    {
        get
        {
            return dictionary.Count;
        }
    }    
    
    // If you try to get a value of a property 
    // not defined in the class, this method is called.
    public override bool TryGetMember(
        GetMemberBinder binder, out object result)
    {
        // Converting the property name to lowercase
        // so that property names become case-insensitive.
        string name = binder.Name.ToLower();

        // If the property name is found in a dictionary,
        // set the result parameter to the property value and return true.
        // Otherwise, return false.
        return dictionary.TryGetValue(binder.Name, out result);
    }

    // If you try to set a value of a property that is
    // not defined in the class, this method is called.
    public override bool TrySetMember(
        SetMemberBinder binder, object value)
    {
        // Converting the property name to lowercase
        // so that property names become case-insensitive.
        dictionary[binder.Name.ToLower()] = value;

        // You can always add a value to a dictionary,
        // so this method always returns true.
        return true;
    }
    
}

class Program
{
    static void Main(string[] args)
    {
        // Creating a dynamic dictionary.
        dynamic person = new DynamicDictionary();

        // Adding new dynamic properties. 
        // The TrySetMember method is called.
        person.FirstName = "Ellen";
        person.LastName = "Adams";

        // Getting values of the dynamic properties.
        // The TryGetMember method is called.
        // Note that property names are case-insensitive.
        Console.WriteLine(person.firstname + " " + person.lastname);

        // Getting the value of the Count property.
        // The TryGetMember is not called, 
        // because the property is defined in the class.
        Console.WriteLine(
            "Number of dynamic properties:" + person.Count);

        // The following statement throws an exception at run time.
        // There is no "address" property,
        // so the TryGetMember method returns false and this causes a
        // RuntimeBinderException.
        // Console.WriteLine(person.address);
    }    
}

// This example has the following output:
// Ellen Adams
// Number of dynamic properties: 2

ExpandoObject.cs

class Program
{
    static void Main(string[] args)
    {
        dynamic employee, manager;

        employee = new ExpandoObject();
        employee.Name = "John Smith";
        employee.Age = 33;

        manager = new ExpandoObject();
        manager.Name = "Allison Brown";
        manager.Age = 42;
        manager.TeamSize = 10;

        WritePerson(manager);
        WritePerson(employee);
    }
    private static void WritePerson(dynamic person)
    {
        Console.WriteLine("{0} is {1} years old.",
                          person.Name, person.Age);
        // The following statement causes an exception
        // if you pass the employee object.
        // Console.WriteLine("Manages {0} people", person.TeamSize);
    }
}
// This code example produces the following output:
// John Smith is 33 years old.
// Allison Brown is 42 years old.

IEnumerablesOnSteroids.cs

public static IEnumerable<int> To(this int from, int to) {
    for (int x = from; x <= to; x++)
        yield return x;
}
public static IEnumerable<int> DownTo(this int from, int to) {
    for (int x = from; x >= to; x--)
        yield return x;
}
public static IEnumerable<int> StepTo(this int from, int to, int step) {
    if (step > 0) {
        for (int x = from; x <= to; x += step)
            yield return x;
    } else if (step < 0) {
        for (int x = from; x >= to; x += step)
            yield return x;
    } else {
        throw new ArgumentException("Step cannot be zero.", "step");
    }
}
public static void Times(this int num, Action<int> action) {
    for (int x = 0; x < num; x++)
        action(x);
}


// Now you can write:

string[] persons = new string[] { "Jack", "Lisa", "Ryan" };
0.To(2).ForEach(i => Console.WriteLine(persons[i]));
//Jack
//Lisa
//Ryan

2.DownTo(0).ForEach(i => Console.WriteLine(persons[i]));
//Ryan
//Lisa
//Jack

0.StepTo(2, 2).ForEach(i => Console.WriteLine(persons[i]));
//Ryan
//Jack
//(run 0 to 2 with step 2)

3.Times(i => Console.WriteLine(persons[i]));
//Jack
//Lisa
//Ryan