BasicObject是所有类的顶级父类

#BasicObject是所有类的顶级父类
class A
end
A.ancestors #=>[A, Object, Kernel, BasicObject]
A.instance_methods.size #=>56,普通的类继承了Object, Kernel, BasicObject类的方法

#通过直接继承BasicObject来获得比较纯净的类
class B<BasicObject
end
B.ancestors #=>[A, BasicObject]
B.instance_methods.size #=>8