扩展类

继承

class Parent
    def hello
        p "Hello Ruby"
    end
end

class Child < Parent
end

=begin
Child = Class.new(Parent)
等价于上面定义继承类的办法
=end

child = Child.new
child.hello

class Parent
  def hello
    p "Hello Ruby"
  end
end

class Child < Parent
  def hello
    p "你好, Ruby"
  end
end

child = Child.new
child.hello
#=> "你好, Ruby" 父类的方法被覆盖了

class Parent
  def hello
    p "Hello Ruby"
  end
end

class Child < Parent
  def hello
    #super相当于php的parent::
    super
    p "你好, Ruby"
  end
end

child = Child.new
child.hello
#=> "Hello Ruby"
#=> "你好, Ruby"

alias与undef

alias

# coding: utf-8
class Parent
  def hello
    p "Hello Ruby"
  end
end

class Child < Parent
  #给父类的方法定义别名，这样就不会和子类方法冲突了
  alias parent_hello hello

  #使用符号也是可以的，随意~
  #alias :parent_hello :hello

  def hello
    p "你好, Ruby"
  end
end

child = Child.new

child.hello
#=> "你好, Ruby"

child.parent_hello
#=> "Hello Ruby"

undef

# coding: utf-8
class Parent
  def hello
    p "Hello Ruby"
  end
end

class Child < Parent
  undef hello
  #undef hello
end

child = Child.new
child.hello
#=> 报错，因为hello方法已经被删除了

单例类

str1 = "Ruby"
str2 = "Ruby"

=begin
Ruby中，所有类都是class类的实例
给class类添加实例方法
=end
class << str1
    def hello
        "Hello, #{self}!"
    end
end

p str1.hello
#=> 成功

p str2.hello
#=> 报错，str2没有hello这个方法