Should I return 'null' or an empty array?

Question

Suppose you have a method that should create and return an array of some sort. What if the array doesn't get populated. Do you return an empty array or null/nothing?

Answer 1

In .NET it's better to return an empty array than null because it saves the caller having to write a null check and/or risking a NullReferenceException; you'll see this is a common pattern in the base class libraries. The only case in which you wouldn't do this is in the unlikely scenario that an empty array and null have different semantic meanings.

The official array usage guidelines state:

The general rule is that null, empty string (""), and empty (0 item) arrays should be treated the same way. Return an empty array instead of a null reference.

That said, if you're using .NET 2.0 or later, it's much better to return an IEnumerable<T> or one of its extensible derivatives such as Collection<T>, ReadOnlyCollection<T>, ICollection<T> or IList<T> (in which case I'd still tend to return an empty one instead of null). More info as to why these should be preferred can be found at Eric Lippert's blog.

Answer 2

I return an empty array - just seems like the right thing to do.