Question

Not that it would be better, but I’m trying to get my head around turning the following method syntax to query syntax to see the difference.

long diskSpace = Directory.EnumerateDirectories(@"c:\")
                    .SelectMany(Directory.EnumerateFiles)
                    .Sum(fileSize => new FileInfo(fileSize).Length);

Answer 1

That query is mostly equivalent to:

long diskSpace = (from directory in Directory.EnumerateDirectories(@"c:\")
                  from file in Directory.EnumerateFiles(directory)
                  select file)
                 .Sum(file => new FileInfo(file).Length);

(I’ve renamed fileSize to file to more accurately represent the meaning, btw.)

There’s one actual difference in this case – we’re creating a new delegate which calls Directory.EnumerateFiles rather than directly creating a delegate from the Directory.EnumerateFiles method group. In other words, it’s one extra level of redirection – but this won’t have any effect on the results and I’d be amazed if it had any significant performance impact.