What is the most efficient way of getting an empty array in C# in terms of time and space?

Question

let's say I need an empty array of a Book class in C#.

public class Book
{
    public string Title { get; set; }
    public Author Author { get; set; }
}

I found the following 3 options to achieve this:

• new Book[0]
• Array.Empty<Book>()
• ArraySegment<Book>.Empty

Can you suggest which one I should go for and the difference between them, please?

Answer 1

In most cases you would use Array.Empty<Book>(). Note that this will return the same instance each time it is called.

new Book[0] will produce a new array. This will require a new object to be allocated, but could be used if you want your array to compare differently to other empty arrays.

ArraySegment<Book>.Empty does not produce an array, but an ArraySegment. ArraySegment is typically used to represent a smaller section of an array. If you should use an ArraySegment or an Array is a more complicated question, especially since there are a wide variety of other collection types to chose between.