Implement Enumerable#slice_after

[jsyeo]

Now that we have the specs for Enumerable#slice_after, we can implement it!

I hope I didn't confuse anyone with the crazy case when usage. Correct me if I am wrong, but I think it's more readable than a bunch of ifs and nil?s.

[jemc]

Might I suggest the following instead:

if pattern_given && block_given?
  raise ArgumentError, "cannot pass both pattern and block"
elsif pattern_given
  block = Proc.new { |elem| pattern === elem }
elsif block_given?
  # use given block
else
  raise ArgumentError, "wrong number of arguments (0 for 1)"
end

I think we should avoid allocating a bunch of unnecessary Arrays if we can (it seems like it would be a performance hit), and I think my example is still just as readable, if not a little more so. The example I gave could be collapsed a bit more into nested ifs, but I care less about that difference.

[jsyeo]

Alright. How about this:

    raise ArgumentError, "cannot pass both pattern and block" if pattern_given && block_given?
    raise ArgumentError, "wrong number of arguments (0 for 1)" if !pattern_given && !block_given?
    block = Proc.new { |elem| pattern === elem } if pattern_given
    # rest of code

[yorickpeterse]

!undefined.equal?(pattern) is more natural.

[yorickpeterse]

Probably should've been more clear with this (my bad), I meant whitespace between every line, not just the one preceding Enumerator.new do ...

[jsyeo]

Ahh... okay got it. 👍

[jsyeo]

@yorickpeterse I've added the newlines. 😄