Question

1. In order to call MyClass::empty().empty
   Do I need to implement an empty method in side MyClass? What would I write inside it?

2. Following, I am not sure how such a call could work: x = MyClass::empty().add("a").add("b")
   Would this be simply calling the add method if it is empty?

Answer 1

What would you write inside it? What do you want it to do?

You’d have a class method named empty that returns something having an empty method that either (a) took no parameters, or (b) had them defaulted.

class MyClass
  def self.empty
    return WithEmpty.new # Or existing WithEmpty
  end
end

It also needs to return something that has an add method, and returns itself.

class WithEmpty
  def initialize
    @a_list = []
  end

  def add x
    @a_list << x
    self
  end

  def empty
    @a_list.empty?
  end
end

It’d be easier/quicker if you described what you’re trying to do. It’s not immediately obvious.

pry(main)> MyClass::empty()
=> #<WithEmpty:0xa01a090 @a_list=[]>
pry(main)> MyClass::empty().empty
=> true
pry(main)> MyClass::empty.empty
=> true
pry(main)> MyClass::empty.add("hi").add("bye")
=> #<WithEmpty:0x9fc8d1c @a_list=["hi", "bye"]>

Now you have no immediate way to get to the “inner” class’s list, unless you saved it in either MyClass (sketchy, since the methods are class, not instance, method), or you save the return value from the last bunch of chained methods.

But if you save the instance, what’s the point of doing it through MyClass? Again, I can’t help but think you need to define what you’re actually trying to accomplish, rather than focusing on how you might accomplish it. What’s the goal?

---

Firstly, there is no “add” method for an array. What you’re describing, as yet, makes no sense, unless you mean something like this:

class MyClass
  def self.empty
    return MyClass.new
  end

  def initialize
    @arr = []
  end

  def empty
    @arr.empty?
  end

  def add x
    @arr << x
    self
  end
end

Then:

pry(main)> MyClass.empty
=> #<MyClass:0x9aea390 @arr=[]>
pry(main)> MyClass.empty.add("ohai").add("kthxbai")
=> #<MyClass:0x99f505c @arr=["ohai", "kthxbai"]>

But again: you’re mixing class and instance methods in a way I don’t find sensical. How do you want to access the array? What’s the point of MyClass? Why not just use an array?

pry(main)> a = []
=> []
pry(main)> a.empty?
=> true
pry(main)> a << "ohai" << "kthxbai"
=> ["ohai", "kthxbai"]
pry(main)> 
pry(main)> a.empty?
=> false

Without any guidelines for what MyClass‘s purpose is, telling you a reasonable way to implement it is difficult, because without context, what you’ve shown doesn’t make a lot of sense.