Ruby 继承但不与超类共享且不共享命名空间的变量/常量

有并没有办法引入具有以下三个属性的变量/常量

a） 当超类未在自己的类中赋值时，它继承超类的值

b） 它不会继承超类以外的其他类的值（即使它们共享名称空间）

c） 当在自己的类中赋值时，它不会覆盖超类的值

使用类实例变量时，a）不满足要求

class A; @foo = :foo end
class B < A; @foo end # => nil  (Does not satisfy (a))
class A; class C; @foo end end # => nil (Satisfies (b))

class B < A; @foo = :bar end
class A; @foo end # => :foo  (Satisfies (c))

class A; @@foo = :foo end
class B < A; @@foo end # => :foo  (Satisfies (a))
class A; class C; @foo end end # => NameError (Satisfies (b))

class B < A; @@foo = :bar end
class A; @foo end # => :bar  (Does not satisfy (c))

class A; Foo = :foo end
class B < A; Foo end # => :foo  (Satisfies (a))
class A; class C; Foo end end # => :foo (Does not satisfy (b))

class B < A; Foo = :bar end
class A; Foo end # => :foo  (Satisfies (c))

A类@foo=：foo结束
B级nil（不满足（a））
甲级；丙级;@foo end#=>nil（满足（b））
B级：foo（满足（c））

使用类变量，c）是不满足的

class A; @foo = :foo end
class B < A; @foo end # => nil  (Does not satisfy (a))
class A; class C; @foo end end # => nil (Satisfies (b))

class B < A; @foo = :bar end
class A; @foo end # => :foo  (Satisfies (c))

class A; @@foo = :foo end
class B < A; @@foo end # => :foo  (Satisfies (a))
class A; class C; @foo end end # => NameError (Satisfies (b))

class B < A; @@foo = :bar end
class A; @foo end # => :bar  (Does not satisfy (c))

class A; Foo = :foo end
class B < A; Foo end # => :foo  (Satisfies (a))
class A; class C; Foo end end # => :foo (Does not satisfy (b))

class B < A; Foo = :bar end
class A; Foo end # => :foo  (Satisfies (c))

A类@@foo=：foo结束
B级：foo（满足（a））
甲级；丙级;@foo end#=>名称错误（满足（b））
B级：条（不满足（c））

使用常数b）不满足要求

class A; @foo = :foo end
class B < A; @foo end # => nil  (Does not satisfy (a))
class A; class C; @foo end end # => nil (Satisfies (b))

class B < A; @foo = :bar end
class A; @foo end # => :foo  (Satisfies (c))

class A; @@foo = :foo end
class B < A; @@foo end # => :foo  (Satisfies (a))
class A; class C; @foo end end # => NameError (Satisfies (b))

class B < A; @@foo = :bar end
class A; @foo end # => :bar  (Does not satisfy (c))

class A; Foo = :foo end
class B < A; Foo end # => :foo  (Satisfies (a))
class A; class C; Foo end end # => :foo (Does not satisfy (b))

class B < A; Foo = :bar end
class A; Foo end # => :foo  (Satisfies (c))

A类；Foo=：Foo结束
B级：Foo（满足（a））
甲级；丙级;；Foo end#=>：Foo（不满足（b））
B级：Foo（满足（c））

我想要这样的东西：

class A; something = :foo end
class B < A; something end # => :foo  (Satisfies (a))
class A; class C; something end end # => nil or Error (Satisfies (b))

class B < A; something = :bar end
class A; something end # => :foo  (Satisfies (c))

A类；something=：foo end
B级零或错误（满足（b））
B级

---

如果不能简单地通过赋值和引用变量/常量来实现，那么有没有办法实现具有此属性的访问器方法？

您需要创建自己类型的具有所需特定属性的访问器。比如说,

module InheritableProperty
  def property
    @property || superclass.property
  end
  def property=(value)
    @property = value
  end
end

class A
  extend InheritableProperty
end
class B < A
  extend InheritableProperty
  class C
    extend InheritableProperty
  end
end

A.property = 1
A.property # => 1
B.property # => 1
B::C.property # error

A.property = 1
B.property = 2
A.property # => 1
B.property # => 2
B::C.property # error

A.property = 1
B.property = 2
B::C.property = 3
A.property # => 1
B.property # => 2
B::C.property # => 3

模块可继承属性
def属性
@属性| |超类.property
结束
def属性=（值）
@属性=值
结束
结束
甲级
扩展可继承属性
结束
B类1
B.属性#=>1
B：：C.属性#错误
A.property=1
B.属性=2
A.属性#=>1
B.属性#=>2
B：：C.属性#错误
A.property=1
B.属性=2
B：：C.property=3
A.属性#=>1
B.属性#=>2
B：：C.属性#=>3

按照约书亚·那不勒斯的建议，我决定这样做：

class A
  def self.foo; defined?(@foo) ? @foo : superclass.foo end
end

class A; @foo = :foo end
class B < A; foo end # => :foo
class A; class C; foo end end # => Error
class B < A; @foo = :bar end
class A; foo end # => :foo

A类
def self.foo；定义？（@foo）@foo:superclass.foo结束
结束
甲级@foo=：foo结束
B级：foo
甲级；丙级;；foo end#=>错误
B级：foo