Does an empty array in .NET use any space?

Question

I have some code where I\'m returning an array of objects.

Here\'s a simplified example:

string[] GetTheStuff() {
    List s = null;
             


        

Answer 1

Even if it's being called "hundreds and hundreds" of times, I'd say it's a premature optimization. If the result is clearer as an empty array, use that.

Now for the actual answer: yes, an empty array takes some memory. It has the normal object overhead (8 bytes on x86, I believe) and 4 bytes for the count. I don't know whether there's anything beyond that, but it's not entirely free. (It is incredibly cheap though...)

Fortunately, there's an optimization you can make without compromising the API itself: have a "constant" of an empty array. I've made another small change to make the code clearer, if you'll permit...

private static readonly string[] EmptyStringArray = new string[0];

string[] GetTheStuff() {
    if( somePredicate() ) {
        List s = new List(); 
        // imagine we load some data or something
        return s.ToArray();
    } else {
        return EmptyStringArray;
    }
}

If you find yourself needing this frequently, you could even create a generic class with a static member to return an empty array of the right type. The way .NET generics work makes this trivial:

public static class Arrays {
    public static readonly Empty = new T[0];
}

(You could wrap it in a property, of course.)

Then just use: Arrays.Empty;

EDIT: I've just remembered Eric Lippert's post on arrays. Are you sure that an array is the most appropriate type to return?