Question

Was there a hook in ruby that is called every time the value of a certain variable changes?

Answer 1

If you write a C extension for Ruby, you can actually make a global variable that triggers a setter hook whenever someone sets it.

But you probably don’t want to do that because you’d have to write some C and it could be a pain to manage that.

A better strategy would be to make it so that the variable is read and set through appropriate methods. Then when the setter method is called you can do whatever you want. Here is an example that encapsulates a variable inside an object:

class Foo
  def bar=(v)
    @bar = v
    # do some stuff
  end

  def bar
    @bar
  end
end

Similarly you could encapsulate the variable in a module or class instead of an object.