corrects Path.size per #58

[mosesn]

motivation

Fixes github issue #58, to the extent that it Path.size will return a None if the length is 0. Semantically, it makes more sense to return a None for an empty file, rather than Some(0), since although a file was found, it was trivial.

issue #58 completeness

Issue #58 mentions that it's unclear whether exists works or not, which is not covered by this pull request. Probably, the issue should be closed, but a new issue should be opened to check that.

testing

I wasn't sure where to put a test in for this, but it should be tested.

different behavior

Previously, Path.size returned Some(0) for files that existed but were empty. Now, it will instead return None.

implementation choices

The existing implementation was a simple one-liner,

if (jfile.exists()) Some(jfile.length()) else None

This was incorrect, but it was unclear how to fix it in a way that preserved its clarity and efficiency. The different ideas I toyed with were

if (jfile.exists() && jfile.length() != 0) Some(jfile.length()) else None

This is the cleanest and the most straightforward, but I think that jfile.length() is not cached, and in the case where the file exists and is nonempty, will have to get a line length twice.

Another idea for how to implement it is to keep this clean system, but instead make it a block.

{
  val length = jfile.length()
  if (jfile.exists() && length != 0) Some(length) else None
}

However, it requires using a block, which is unsightly.

Ultimately, I decided to go with something that looks ok, and that I guessed the compiler would probably optimize away anyway. The biggest concern was to bind jfile.length() to a variable so that I didn't have to call it twice, so I used a match expression, which lets me both check its value and binds its contents.

if (jfile.exissts()) jfile.length() match {
  case 0 => None
  case nonzero => Some(nonzero)
} else None

The value of the "if" part of the expression being a match expression is a little messy, which is distasteful, but I felt like adding another set of curly braces was worse.