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public class MessageBus
{
    public void Send(IMessage message)
    {
        //Sends a single message. 
    }

    public void SendAll(List<IMessage> messages)
    {
        foreach (var message in messages)

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public void SendAll(IEnumerable<IMessage> messages)
{
    foreach (var message in messages)
        Send(message);
}

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public interface IEnumerable<out T> : IEnumerable
{
    IEnumerator<T> GetEnumerator()
}

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public interface IMessage { }

public class RemoveOrderLineItem : IMessage { }

public class MessageBus
{
    public void Send(IMessage message)
    {
        //Send the message.
    }

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//When you write:
public enum Role
{
    System,
    Manager,
    Employee,
    HumanResources
}

//...the compiler assumes you wrote:

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Role manager = (Role)(1);
Role bogus = (Role)(-1);

Console.WriteLine(manager);
Console.WriteLine(bogus);

//Output:
//  Manager
//  -1

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public class Role : Enumeration<Role>
{
    public static readonly Role System = new Role(0, "System", "System", true);
    public static readonly Role Manager = new Role(1, "Manager", "Michelle", false);
    public static readonly Role Employee = new Role(2, "Employee", "Eric", false);
    public static readonly Role HumanResources = new Role(3, "Human Resources", "Harry", false);
    
    private Role(int value, string displayName, string personaName, bool testrole)
        : base(value, displayName)
    {

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class Enumeration<TEnumeration> 
    where TEnumeration : Enumeration<TEnumeration>

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public void ReceiveLambdaAsDelegate(Func<int, int> function) {...}

public void ReceiveLambdaAsExpression(Expression<Func<int, int>> expression) {...}

...

ReceiveLambdaAsDelegate(x => x*x);
ReceiveLambdaAsExpression(x => x*x);

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public void ReceiveLambdaAsDelegate(Func<int, int> function) {...}

public void ReceiveLambdaAsExpression(Expression<Func<int, int>> expression) {...}

...

ReceiveLambdaAsDelegate(x => x*x);
ReceiveLambdaAsExpression(x => x*x);