Info Catalog eieio: Generics eieio: Writing Methods eieio: Static Methods

eieio: Methods

 
 6.2 Methods
 ===========
 
 A method is a function that is executed if the first argument passed to
 it matches the method’s class.  Different EIEIO classes may share the
 same method names.
 
    Methods are created with the ‘defmethod’ macro, which is similar to
 ‘defun’.
 
  -- Macro: defmethod method [:before | :primary | :after | :static ]
           arglist [doc-string] forms
 
      METHOD is the name of the function to create.
 
      ‘:before’ and ‘:after’ specify execution order (i.e., when this
      form is called).  If neither of these symbols are present, the
      default priority is used (before ‘:after’ and after ‘:before’);
      this default priority is represented in CLOS as ‘:primary’.
 
      Note: The ‘:BEFORE’, ‘:PRIMARY’, ‘:AFTER’, and ‘:STATIC’ method
      tags were in all capital letters in previous versions of EIEIO.
 
      ARGLIST is the list of arguments to this method.  The first
      argument in this list—and _only_ the first argument—may have a type
      specifier (see the example below).  If no type specifier is
      supplied, the method applies to any object.
 
      DOC-STRING is the documentation attached to the implementation.
      All method doc-strings are incorporated into the generic method’s
      function documentation.
 
      FORMS is the body of the function.
 
 In the following example, we create a method ‘mymethod’ for the
 ‘classname’ class:
 
      (defmethod mymethod ((obj classname) secondarg)
        "Doc string" )
 
 This method only executes if the OBJ argument passed to it is an EIEIO
 object of class ‘classname’.
 
    A method with no type specifier is a “default method”.  If a given
 class has no implementation, then the default method is called when that
 method is used on a given object of that class.
 
    Only one default method per execution specifier (‘:before’,
 ‘:primary’, or ‘:after’) is allowed.  If two ‘defmethod’s appear with
 ARGLISTs lacking a type specifier, and having the same execution
 specifier, then the first implementation is replaced.
 
    When a method is called on an object, but there is no method
 specified for that object, but there is a method specified for object’s
 parent class, the parent class’ method is called.  If there is a method
 defined for both, only the child’s method is called.  A child method may
 call a parent’s method using ‘call-next-method’, described below.
 
    If multiple methods and default methods are defined for the same
 method and class, they are executed in this order:
 
   1. method :before
   2. default :before
   3. method :primary
   4. default :primary
   5. method :after
   6. default :after
 
    If no methods exist, Emacs signals a ‘no-method-definition’ error.
 Signals.
 
  -- Function: call-next-method &rest replacement-args
 
      This function calls the superclass method from a subclass method.
      This is the “next method” specified in the current method list.
 
      If REPLACEMENT-ARGS is non-‘nil’, then use them instead of
      ‘eieio-generic-call-arglst’.  At the top level, the generic
      argument list is passed in.
 
      Use ‘next-method-p’ to find out if there is a next method to call.
 
  -- Function: next-method-p
      Non-‘nil’ if there is a next method.  Returns a list of lambda
      expressions which is the ‘next-method’ order.
 
    At present, EIEIO does not implement all the features of CLOS:
 
   1. There is currently no ‘:around’ tag.
   2. CLOS allows multiple sets of type-cast arguments, but EIEIO only
      allows the first argument to be cast.
 

Info Catalog eieio: Generics eieio: Writing Methods eieio: Static Methods