Subclases y Herencia

• Si cuando se define una clase no se especifica una superclase entonces nuestra clase hereda implíctamente de Object.

• The fact that classes may have multiple subclasses but only a single superclass (single inheritance) means that they can be arranged in a tree structure, which we call the Ruby class hierarchy.
• The BasicObject class is the root of this hierarchy, and every class inherits directly or indirectly from Object.
• The descendants of a class are the subclasses of the class plus the subclasses of the subclasses, and so on recursively.
• The ancestors of a class are the superclass, plus the superclass of the superclass, and so on up to Object.
• The syntax for extending a class is simple. Just add a < character and the name of the superclass to your class statement.

  We then create a subclass using class Child < Parent. The < notation means we’re creating a subclass of the thing on the right; the fact that we use less-than presumably signals that the child class is supposed to be a specialization of the parent.

  class Point3D < Point    # Define class Point3D as a subclass of Point
  end
  

• Es posible heredar de una subclase definida mediante Struct:

  [~/rubytesting/TheRubyProgrammingLanguage/Chapter7ClassesAndModules]$ cat subclassing_a_struct.rb 
  class Punto < Struct.new("Point3D", :x, :y, :z)
    # Superclass struct give us accessor methods, ==, to_s, etc.
     def modulo
       Math.sqrt(x*x+y*y+z*z)
     end
  end
  if $0 == __FILE__
    p = Punto.new(1,2,3)
    puts p.x
    puts p.modulo
  end
  

  Ejecución:

  [~/rubytesting/TheRubyProgrammingLanguage/Chapter7ClassesAndModules]$ ruby subclassing_a_struct.rb 
  1
  3.7416573867739413