Alternative to IEnumerable for read-only collections

.NET 4.5 introduced a new interface which is great if you want to expose a collection as readonly.

The problem with IEnumerable<T> is that it’s forward only. i.e. there is no guarantee that you can traverse it multiple times. The collection size might also be unknown, depending on the implementation.

So if you want to expose a collection which can be traversed multiple times and where the size is know there is as of .NET 4.5 another alternative. And that’s IReadOnlyList<T>. It inherits another new interface called IReadOnlyCollection<out T>.

Code

public interface IReadOnlyCollection<out T> 
      : IEnumerable<T>, 
        IEnumerable
{
    int Count { get; }
}
public interface IReadOnlyList<out T> 
      : IReadOnlyCollection<T>
      , IEnumerable<T>
      , IEnumerable
{
    T this[int index] { get; }
}

Usage example

public class MyRepository
{
    public IReadOnlyList<User> FindUsers(string lastName)
    {
        // [...]
    }

    // [...]
}



Throwing exceptions

Throwing exceptions is in itself trivial. Just invoke throw with an exception object. But when should you throw? Should you create a new exception or rethrow an old one? What should you include in the exception info?

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What are exceptions?

This blog has been quiet for a while. I am currently writing a book about localization. Me and my partner is also getting close to release of our new startup. One of it’s features is to automatically catch unhandled exceptions and send them to a webservice for analytics. But to take full advantage of that you’ll have to use a set of exception handling best practices. I’m therefore going to write a set of exception articles. The series will end with the release of our service.

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More relevant ads please.

I just read that Mozilla are going to block third party cookies in the next version of Firefox (optional, but blocking is on per default). That’s great. Let’s get rid of the web site/usage tracking that all advertising services has.

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Azure shut me down again

Yet again I got shut down by Azure. This time the CPU quote was exceeded just a couple of hours into the new quota period.

I’ve switched to “Reserved” mode which doesn’t have the same limits (which is not said anywhere in the management interface).


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