Info Catalog eieio: Basic Methods eieio: Default Superclass

eieio: Signal Handling

 
 15.3 Signal Handling
 ====================
 
 The default superclass defines methods for managing error conditions.
 These methods all throw a signal for a particular error condition.
 
    By implementing one of these methods for a class, you can change the
 behavior that occurs during one of these error cases, or even ignore the
 error by providing some behavior.
 
  -- Function: slot-missing object slot-name operation &optional
           new-value
      Method invoked when an attempt to access a slot in OBJECT fails.
      SLOT-NAME is the name of the failed slot, OPERATION is the type of
      access that was requested, and optional NEW-VALUE is the value that
      was desired to be set.
 
      This method is called from ‘oref’, ‘oset’, and other functions
      which directly reference slots in EIEIO objects.
 
      The default method signals an error of type ‘invalid-slot-name’.
      Signals.
 
      You may override this behavior, but it is not expected to return in
      the current implementation.
 
      This function takes arguments in a different order than in CLOS.
 
  -- Function: slot-unbound object class slot-name fn
      Slot unbound is invoked during an attempt to reference an unbound
      slot.  OBJECT is the instance of the object being reference.  CLASS
      is the class of OBJECT, and SLOT-NAME is the offending slot.  This
      function throws the signal ‘unbound-slot’.  You can overload this
      function and return the value to use in place of the unbound value.
      Argument FN is the function signaling this error.  Use
      “slot-boundp” to determine if a slot is bound or not.
 
      In CLOS, the argument list is (CLASS OBJECT SLOT-NAME), but EIEIO
      can only dispatch on the first argument, so the first two are
      swapped.
 
  -- Function: no-applicable-method object method &rest args
      Called if there are no implementations for OBJECT in METHOD.
      OBJECT is the object which has no method implementation.  ARGS are
      the arguments that were passed to METHOD.
 
      Implement this for a class to block this signal.  The return value
      becomes the return value of the original method call.
 
  -- Function: no-next-method object &rest args
      Called from “call-next-method” when no additional methods are
      available.  OBJECT is othe object being called on
      “call-next-method”.  ARGS are the arguments it is called by.  This
      method signals “no-next-method” by default.  Override this method
      to not throw an error, and its return value becomes the return
      value of “call-next-method”.
 

Info Catalog eieio: Basic Methods eieio: Default Superclass