String Calculator Kata - Ruby version

This Code Kata is Roy Osherove's String Calculator. See http://osherove.com/tdd-kata-1

At my previous employer, in 2014-2015, we used to practice Code Katas with a twist:

Live coding in front of an audience of fellow programmers!

Sessions were fun (the Thursdays during the Brown Bag time-slot), and it was a good way to discover new languages and paradigms. We coded the String Calculator with at least 20 different languages, from x86 Assembly (yes) to Monadic Parsers in Haskell via RPG (Arhh!), Rust, Elixir and many more (including the more common languages obviously).

Even if we would have practiced the Kata on our own before, to be in the hot seat was always pushing people out of their comfort zone.

Live Coding Version - 4 Lines

The version I coded during the live coding Brown Bag session, using TDD: write the test, fail, write the code, refactor.

This is not readable, and not the way I leave code behind, I just wanted something terse to contrast with other languages.

def add(str)
  dlm = str[%r{//(\[.*?\])\n}] ? $1.scan(/\[(.*?)\]/).flatten.map { |d| Regexp.quote(d) }.join('|') : ','
  ns = str.split(/#{dlm}|\n/).map(&:to_i)
  raise ArgumentError, "Negatives Not Allowed: #{ns.select { |n| n < 0 }.join(',') }" if ns.find { |n| n < 0 }
  ns.reject { |n| n > 1000 }.reduce(0, :+)
end

One Liner Version

def add(s)
  s.split(/#{s[%r{//(\[.*?\])\n}]?$1.scan(/\[(.*?)\]/).flatten.map{|d|Regexp.quote(d)}.join('|'):','}|\n/).map(&:to_i).select{|n|n<0?(fail ArgumentError,"Negs errors:#{s.scan(/-\d+/).join(',')}"):n}.reject{|n|n>1000}.reduce(0,:+)
end

Note that there is no semi-colon, and so a true one liner (not a group of statements joined on one line - that would have been cheating!)

Tests

# Tests - RSpec
describe "StringCalculator.add" do
  it 'should return 0 for empty string' do
    expect(add("")).to eql(0)
  end

  it 'should return value for one number' do
    expect(add("1")).to eql(1)
  end

  it 'should return sum of 2 numbers' do
    expect(add("1,2")).to eql(3)
  end

  it 'should return sum of multiple numbers' do
    expect(add("1,2,3,4,5,6,7,8,9")).to eql(45)
  end

  it 'should handle new line as delimiter' do
    expect(add("1,2\n3")).to eql(6)
  end

  it 'should be able to specify new delimiter' do
    expect(add("//[;]\n1;2\n3")).to eql(6)
  end

  it 'should raise an exception for negative numbers' do
    expect { add("-1,2\n-3") }.to raise_error ArgumentError, /-1,-3/
  end

  it 'should ignore number greater than 1000' do
    expect(add("1001,2\n3000")).to eql(2)
  end

  it 'should handle delimiter of multiple length' do
    expect(add("//[;;;]\n1;;;2\n3")).to eql(6)
  end

  it 'should handle multiple delimiters of multiple lengths' do
    expect(add("//[;;;][$$$]\n1;;;2$$$3")).to eql(6)
  end
end