module ActiveModel::Validations::ResolveValue

def resolve_value(record, value)
  case value
  when Proc
    if value.arity == 0
      value.call
    else
      value.call(record)
    end
  when Symbol
    record.send(value)
  else
    if value.respond_to?(:call)
      value.call(record)
    else
      value
    end
  end
end