What is the difference between Directory.EnumerateFiles vs Directory.GetFiles?

From the docs:

The EnumerateFiles and GetFiles methods differ as follows: When you use EnumerateFiles, you can start enumerating the collection of names before the whole collection is returned; when you use GetFiles, you must wait for the whole array of names to be returned before you can access the array. Therefore, when you are working with many files and directories, EnumerateFiles can be more efficient.

So basically, EnumerateFiles returns an IEnumerable which can be lazily evaluated somewhat, whereas GetFiles returns a string[] which has to be fully populated before it can return.

When using EnumerateFiles, all speed is lost if you are then using .Last. This makes sense of course, because to get to the last file, it will need to enumerate all files, then grab the last one.

However, using .First or .FirstOrDefault becomes very fast, because it simply grabs the first item and moves on.

EnumerateFiles returns IEnumerable<string> and that implies deferred execution. It is only available in .net 4 and up.

As the File system is notoriously slow (especially for large folders) the deferred execution can be a real bonus for sequential processing. Depending on lots of other factors.