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remcopeereboom's solution

to Phone Number in the Ruby Track

Published at Jul 13 2018 · 2 comments
Test suite


This solution was written on an old version of Exercism. The tests below might not correspond to the solution code, and the exercise may have changed since this code was written.

Clean up user-entered phone numbers so that they can be sent SMS messages.

The North American Numbering Plan (NANP) is a telephone numbering system used by many countries in North America like the United States, Canada or Bermuda. All NANP-countries share the same international country code: 1.

NANP numbers are ten-digit numbers consisting of a three-digit Numbering Plan Area code, commonly known as area code, followed by a seven-digit local number. The first three digits of the local number represent the exchange code, followed by the unique four-digit number which is the subscriber number.

The format is usually represented as


where N is any digit from 2 through 9 and X is any digit from 0 through 9.

Your task is to clean up differently formatted telephone numbers by removing punctuation and the country code (1) if present.

For example, the inputs

  • +1 (613)-995-0253
  • 613-995-0253
  • 1 613 995 0253
  • 613.995.0253

should all produce the output


Note: As this exercise only deals with telephone numbers used in NANP-countries, only 1 is considered a valid country code.

For installation and learning resources, refer to the exercism help page.

For running the tests provided, you will need the Minitest gem. Open a terminal window and run the following command to install minitest:

gem install minitest

If you would like color output, you can require 'minitest/pride' in the test file, or note the alternative instruction, below, for running the test file.

Run the tests from the exercise directory using the following command:

ruby phone_number_test.rb

To include color from the command line:

ruby -r minitest/pride phone_number_test.rb


Event Manager by JumpstartLab http://tutorials.jumpstartlab.com/projects/eventmanager.html

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.


require 'minitest/autorun'
require_relative 'phone_number'

# Common test data version: 1.2.0 39cba0d
class PhoneNumberTest < Minitest::Test
  def test_cleans_the_number
    # skip
    assert_equal "2234567890", PhoneNumber.clean("(223) 456-7890")

  def test_cleans_numbers_with_dots
    assert_equal "2234567890", PhoneNumber.clean("223.456.7890")

  def test_cleans_numbers_with_multiple_spaces
    assert_equal "2234567890", PhoneNumber.clean("223 456   7890   ")

  def test_invalid_when_9_digits
    assert_nil PhoneNumber.clean("123456789")

  def test_invalid_when_11_digits_does_not_start_with_a_1
    assert_nil PhoneNumber.clean("22234567890")

  def test_valid_when_11_digits_and_starting_with_1
    assert_equal "2234567890", PhoneNumber.clean("12234567890")

  def test_valid_when_11_digits_and_starting_with_1_even_with_punctuation
    assert_equal "2234567890", PhoneNumber.clean("+1 (223) 456-7890")

  def test_invalid_when_more_than_11_digits
    assert_nil PhoneNumber.clean("321234567890")

  def test_invalid_with_letters
    assert_nil PhoneNumber.clean("123-abc-7890")

  def test_invalid_with_punctuations
    assert_nil PhoneNumber.clean("123-@:!-7890")

  def test_invalid_if_area_code_does_not_start_with_2_9
    assert_nil PhoneNumber.clean("(123) 456-7890")

  def test_invalid_if_exchange_code_does_not_start_with_2_9
    assert_nil PhoneNumber.clean("(223) 056-7890")

  # Problems in exercism evolve over time, as we find better ways to ask
  # questions.
  # The version number refers to the version of the problem you solved,
  # not your solution.
  # Define a constant named VERSION inside of the top level BookKeeping
  # module, which may be placed near the end of your file.
  # In your file, it will look like this:
  # module BookKeeping
  #   VERSION = 1 # Where the version number matches the one in the test.
  # end
  # If you are curious, read more about constants on RubyDoc:
  # http://ruby-doc.org/docs/ruby-doc-bundle/UsersGuide/rg/constants.html

  def test_bookkeeping
    assert_equal 2, BookKeeping::VERSION
class PhoneNumber
  attr_reader :number

  BAD_NUMBER = '0000000000'

  def initialize(phone_number)
    @number = phone_number.chars.select{ |x| x =~ /\w/ }.join
    @number = @number[/^1?(\d{10})$/, 1]
    @number ||= BAD_NUMBER

  def area_code
    number[0, 3]

  def local_number
    "#{number[3, 3]}-#{number[6,4]}"

  def to_s
    "(#{area_code}) #{local_number}"

Community comments

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Avatar of Mzuleta4

could you tell me what it's for || =?

Avatar of remcopeereboom

@Mzuleta4 commented:

could you tell me what it's for || =?

a ||= b is syntactic sugar for a = a || b. This is a way to do "memoization" for non-falsey types (basically anything but nil and false). If a is already initialized (to a non-falsey value), than a || b will short-circuit evaluate and never evaluate b. The expression a || b will then return a, so a gets assigned to a But if a is undefined, then evaluating a will return nil wich is treated as false, so b gets evaluated and the result of that will be assigned to a.

Here is a more verbose way of writing the same thing: a = b if a.nil?

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