Count comments and lines of code in ruby

Question

Hi I wrote a small script as an answer for a stack overflow question, that counts lines of code and comments (in C and C++ style).

f = File.open("test.txt")

loc = 0
comments = 0
while line = f.gets
  if commented ||= line.match(/^\/\*/)
    commented = nil if line.match(/\*\/$/)
    comments += 1
  elsif line.match(/^\s*\/\//)
    comments += 1
  else
    loc +=1 unless line.match(/^\s*\n/)
  end
end

puts loc
puts comments

I'm just looking for some feedback/review.

Answer 1

Your code looks pretty good to me, only that it's very imperative. I know it's not for everybody's taste, but a functional approach on text processing is also feasible.

My take: you start by defining an object (which may be a hash) to store the state (needed for in intermediate iterations and the final result), and then fold (reduce/inject) over the input lines, returning the next state on each step.

There are some edge cases (lines with multiple or nested comment) which I won't consider, let's keep it simple. I'd write:

initial_state = {lines: 0, comments: 0, in_multiline_comment: false}
final_state = open("test.txt").lines.inject(initial_state) do |state, line|
  state_update = if state[:in_multiline_comment]
    {comments: state[:comments] + 1, in_multiline_comment: !line.match(/\*\//)}
  else
    case line 
    when /\/\*/
      {comments: state[:comments] + 1, in_multiline_comment: !line.match(/\*\//)}
    when /\/\//
      {comments: state[:comments] + 1}
    else
      {lines: state[:lines] + (line.strip.empty? ? 0 : 1)}
    end
  end
  state.merge(state_update)
end

Notice that you don't worry about stateful variables anymore, we just think "if I have this input and this current state, what output would I want?". Once you've covered all scenarios, the algorithm is done (hopefully leaving behind a declarative and maintainable code).