module Interface
  # General basis for an interface
  
  NotImplemented = Class.new ArgumentError
  # Indicates a target object does not implement the checked interface
  MissingMethod = Class.new ArgumentError
  # Raised when a method from the interface is not supported by the implementation
  InvalidReturn = Class.new ArgumentError
  # Raised when the target return value does not meet the expectaions on it.

  # Check if an interface is implemented on a target
  # Checked by seeing if the interface module is fronting the ancesor chain
  def implemented_on?(target)
    target.class.ancestors.first == self
  end

  # Enforce a target implements the interface
  def required_on!(target)
    raise NotImplemented unless self.implemented_on? target
  end

end