Source Code Reading

default_value.rb

define_method(abbr) { |date = nil| DatePart.new(abbr, date) }

group_by.rb

names = [ 'Giuseppe', 'Giulia', 'Luca', 'Andrea', 'Roberto' ]
grouped_by_first_letter = names.group_by { |name| name[0] }

puts grouped_by_first_letter
# >> {"G"=>["Giuseppe", "Giulia"], "L"=>["Luca"], "A"=>["Andrea"], "R"=>["Roberto"]}

module_eval.rb

module MyModule
  chars = %w(A B C)
  words = chars.permutation.to_a
  
  words.each do |word|
    method_name = word.join
    module_eval(<<-PERMUTATION, __FILE__, __LINE__)
      def #{method_name}
        puts "#{word}"
      end
    PERMUTATION
  end
end

include MyModule

abc  # => nil
# >> a
# >> b
# >> c

words_generator.rb

chars = %w(A B C)
words = chars.permutation.to_a
# => [["A", "B", "C"],
#     ["A", "C", "B"],
#     ["B", "A", "C"],
#     ["B", "C", "A"],
#     ["C", "A", "B"],
#     ["C", "B", "A"]]

words_generator_2.rb

chars = %w(A B C)
words = chars.permutation(2).to_a
# => [["A", "B"], ["A", "C"], ["B", "A"], ["B", "C"], ["C", "A"], ["C", "B"]]