class ViewModel::References

A bucket for configuration, used for serializing and deserializing.

def add_reference(value)

it by calling the given block.
under which the data is stored. If the data is not present, will compute
Takes a reference to a thing that is to be shared, and returns the id 
def add_reference(value)
  ref = @ref_by_value[value]
  unless ref.present?
    ref = new_ref!(value)
    @ref_by_value[value] = ref
    @value_by_ref[ref] = value
  end
  ref
end

def clear! 

def clear!
  @ref_by_value.clear
  @value_by_ref.clear
end

def has_references? 

def has_references?
  @ref_by_value.present?
end

def initialize 

def initialize
  @last_ref = 0
  @ref_by_value = {}
  @value_by_ref = {}
end

def new_ref!(viewmodel)

Ensure stable reference ids for the same (persisted) viewmodels. 
def new_ref!(viewmodel)
  vm_ref = viewmodel.to_reference
  if vm_ref.model_id
    hash = Digest::SHA256.base64digest("#{vm_ref.viewmodel_class.name}.#{vm_ref.model_id}")
    "ref:h:#{hash}"
  else
    format('ref:i:%06<count>d', count: (@last_ref += 1))
  end
end