Module, Mixins und Enumerable

module Geometrie
  PI = 3.14159
  def self.kreisflaeche(r) = PI * r * r
  class Kreis
    def initialize(r) = @r = r
    def flaeche = Geometrie.kreisflaeche(@r)
  end
end

puts Geometrie.kreisflaeche(2)
puts Geometrie::Kreis.new(1).flaeche
puts Geometrie::PI

12.56636
3.14159
3.14159

module Begruessung
  def hallo = "Hallo, ich bin #{name}"
end

module Laufend
  def laufe = "#{name} läuft"
end

class Mensch
  include Begruessung, Laufend
  attr_reader :name
  def initialize(name) = @name = name
end

m = Mensch.new("Mia")
puts m.hallo, m.laufe
p Mensch.ancestors.first(4), m.is_a?(Begruessung)

Hallo, ich bin Mia
Mia läuft
[Mensch, Begruessung, Laufend, Object]
true

module Zaehler
  def zaehle = @n = (@n || 0) + 1
end
module Info
  def info = "Klasse #{name}"
end
module Laut
  def sprich = super.upcase
end

class Robot
  include Zaehler
  extend Info
  prepend Laut
  def sprich = "piep"
end
r = Robot.new
r.zaehle
puts r.zaehle, Robot.info, r.sprich

2
Klasse Robot
PIEP

class Regal
  include Enumerable
  def initialize(*buecher) = @buecher = buecher
  def each(&block)
    return to_enum(:each) unless block
    @buecher.each(&block)
    self
  end
end

r = Regal.new("Faust", "Emil", "Momo", "Ronja")
p r.sort, r.map(&:length), r.select { |b| b.length == 4 }, r.min_by(&:length), r.first(2)
p r.include?("Momo"), r.each_slice(2).to_a, r.sum(&:length), r.to_a.last, r.each_with_index.to_a.first
p r.lazy.map(&:upcase).first(2), r.reduce { |a, b| a.length > b.length ? a : b }

["Emil", "Faust", "Momo", "Ronja"]
[5, 4, 4, 5]
["Emil", "Momo"]
"Emil"
["Faust", "Emil"]
true
[["Faust", "Emil"], ["Momo", "Ronja"]]
18
"Ronja"
["Faust", 0]
["FAUST", "EMIL"]
"Ronja"

class Fibonacci
  include Enumerable
  def each
    a, b = 0, 1
    loop do
      yield a
      a, b = b, a + b
    end
  end
end
p Fibonacci.new.lazy.select(&:even?).first(5)
p Fibonacci.new.take(10)

zaehler = Enumerator.new do |y|
  n = 0
  loop { y << (n += 1) }
end
p zaehler.take(3), zaehler.next, zaehler.next, zaehler.peek

[0, 2, 8, 34, 144]
[0, 1, 1, 2, 3, 5, 8, 13, 21, 34]
[1, 2, 3]
1
2
3