Question

In Ruby, is there a way to ‘override’ a constant in a subclass in such a way that calling an inherited method from the subclass results in that method using the new constant instead of the old one? For example:

class SuperClass
  CONST = "Hello, world!"
  def self.say_hello
    CONST
  end
end

class SubClass < SuperClass
  override_const :CONST, "Hello, Bob!"
end

SuperClass.say_hello # => "Hello, world!"
SubClass.say_hello   # => "Hello, Bob!"

If not, is there perhaps a way to do something like this instead?

class SuperClass
  CONST = "Hello, world!"
  def self.say_hello
    CONST
  end
end

SubClass = SuperClass.clone
SubClass.send(:remove_const, :CONST)
SubClass.const_set(:CONST, "Hello, Bob!")

SubClass.say_hello # => "Hello, Bob!"

---

Note: I tried my second example out in irb, and it seems to work except that class methods can’t seem to access CONST after I clone the class:

irb(main):012:0> SubClass.say_hello
NameError: uninitialized constant Class::CONST
        from (irb):4:in `say_hello'
        from (irb):12
        from C:/Ruby193/bin/irb:12:in `<main>'

Answer 1

I’ve done this by simply redefining the constant in the subclass, and then referring to it in methods as self.class::CONST in instance methods and self::CONST in class methods. In your example:

class SuperClass
  CONST = "Hello, world!"
  def self.say_hello
    self::CONST
  end
end

class SubClass < SuperClass
  CONST = "Hello, Bob!"
end

SubClass.say_hello #=> "Hello, Bob!"