Join/Split with arbitrary single-char dlimiter

delim.rb

def join(strings, delimiter)
  raise ArgumentError, "Invalid delimiter \"\\\"" if delimiter == "\\"

  strings.map do |s|
    s.gsub(/(\\|#{Regexp.escape(delimiter)})/, '\\\\\1')
  end.join(delimiter)
end

def split(string, delimiter)
  raise ArgumentError, "Invalid delimiter \"\\\"" if delimiter == "\\"

  strings = []
  token = nil
  literal = false

  string.chars.each do |char|
    token ||= ""

    if literal
      token += char
      literal = false
      next
    end

    case char
    when "\\"
      literal = true
    when delimiter
      strings << token
      token = ""
    else
      token += char
    end
  end

  raise ArgumentError, "dangling escape" if literal

  strings << token unless token.nil?

  strings
end

test.rb

require_relative './delim'

# { delimiter => { string => array , ... }, ... }
# for each string/array pair S/A:
#  - join(A) == S
#  - split(S) == A
test_cases = {
  ":" => {
    "" => [],
    "foo" => ["foo"],
    ":" => ["", ""],
    "foo:bar" => ["foo", "bar"],
    'foo\:bar' => ["foo:bar"],
    "foo:" => ["foo", ""],
    "foo:bar:" => ["foo", "bar", ""],
    ':foo\::\:bar:\:::' => ["", "foo:", ":bar", ":", "", ""],
    "\\\\:foo" => ["\\", "foo"],
    "\\\\\\:foo" => ["\\:foo"],
    "foo\\\\\\:\\\\bar" => ["foo\\:\\bar"]
  },
  # Regex character
  "|" => {
    "" => [],
    "foo" => ["foo"],
    "|" => ["", ""],
    "foo|bar" => ["foo", "bar"],
    'foo\|bar' => ["foo|bar"],
    "foo|" => ["foo", ""],
    "foo|bar|" => ["foo", "bar", ""],
    '|foo\||\|bar|\|||' => ["", "foo|", "|bar", "|", "", ""],
    "\\\\|foo" => ["\\", "foo"],
    "\\\\\\|foo" => ["\\|foo"],
    "foo\\\\\\|\\\\bar" => ["foo\\|\\bar"]
  },
  " " => {
    "" => [],
    "foo" => ["foo"],
    "   " => ["", "", "", ""],
    ' \  ' => ["", " ", ""],
    "this is a test" => ["this", "is", "a", "test"],
    %q[\ this\ is a\ test\ ] => [" this is", "a test "]
  },
  "\n" => {
    "" => [],
    "\n" => ["", ""],
    "foo\nbar" => ["foo", "bar"],
    "foo\\\nbar" => ["foo\nbar"],
    "\nfoo\\\nbar\n" => ["", "foo\nbar", ""]
  }
}

test_cases.each do |delimiter, cases|
  cases.each do |str, arr|
    got = split(str, delimiter)
    if got != arr
      puts "split(#{str.inspect}, #{delimiter.inspect}): Got #{got.inspect}, want #{arr.inspect}"
    end
  end

  cases.each do |str, arr|
    got = join(arr, delimiter)
    if got != str
      puts "join(#{arr.inspect}, #{delimiter.inspect}): Got #{got.inspect}, want #{str.inspect}"
    end
  end
end