about_keyword_arguments.rb

require File.expand_path(File.dirname(__FILE__) + "/neo")

# TIL:
# - Methods with named parameters can be called without any arguments and the values belonging to the parameters will be
#   used by default.
#
# - Methods can have mandatory parameters and optional parameters but the optional params must come after the named ones.
# - By providing a named parameter without a value, you make it a mandatory named parameter.

class AboutKeywordArguments < Neo::Koan
  def method_with_keyword_arguments(one: 1, two: "two")
    [one, two]
  end

  def test_keyword_arguments
    assert_equal Array, method_with_keyword_arguments.class
    assert_equal [1, "two"], method_with_keyword_arguments
    assert_equal ["one", "two"], method_with_keyword_arguments(one: "one")
    assert_equal [1, 2], method_with_keyword_arguments(two: 2)
  end

  def method_with_keyword_arguments_with_mandatory_argument(one, two: 2, three: 3)
    [one, two, three]
  end

  def test_keyword_arguments_with_wrong_number_of_arguments
    exception = assert_raise(ArgumentError) do
      method_with_keyword_arguments_with_mandatory_argument
    end
    assert_match(/wrong number of arguments/, exception.message)
  end

  def method_with_mandatory_keyword_arguments(one:, two: "two")
    [one, two]
  end

  def test_mandatory_keyword_arguments
    assert_equal ["one", "two"], method_with_mandatory_keyword_arguments(one: "one")
    assert_equal [1, 2], method_with_mandatory_keyword_arguments(two: 2, one: 1)
  end

  def test_mandatory_keyword_arguments_without_mandatory_argument
    exception = assert_raise(ArgumentError) do
      method_with_mandatory_keyword_arguments
    end
    assert_match(/missing keyword: :one/, exception.message)
  end
end