[InAnEmergency]

Ruby's `Pathname#absolute?` is doing a lot more work[1]. I don't know why, but it is.

If I change it to just check the first character for the file separator, as I understand FasterPath does, then of course it is faster:

    Warming up --------------------------------------
                original     4.109k i/100ms
                  faster   110.202k i/100ms
    Calculating -------------------------------------
                original     42.645k (± 3.7%) i/s -    213.668k in   5.017595s
                  faster      2.643M (± 4.4%) i/s -     13.224M in   5.013294s

    Comparison:
                  faster:  2643274.6 i/s
                original:    42644.5 i/s - 61.98x slower

My implementation:

    class Pathname
      def f_relative?
        @path[0] != File::SEPARATOR
      end
    end

[1] https://github.com/ruby/ruby/blob/68ebbbfebe5b666cf76ab41f1e...

[33degrees]

A quick look at the tests[1] shows that it handles drive letters. The current implementation is probably not the most efficient though...

[1] https://github.com/ruby/ruby/blob/68ebbbfebe5b666cf76ab41f1e...

[munificent]

That returns a wrong result on Windows paths, and throws an exception on the empty string.

There are a ton of edge cases in path manipulation code.

[kevincox]

I'm pretty sure his implementation works on empty strings because `str[0].nil?`. So the comparison is false, giving the right (?) answer.