eieio / eieio-base.el

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;;; eieio-base.el --- Base classes for EIEIO.

;; Copyright (C) 2000, 2001, 2002 Eric M. Ludlam
;; Author: <>
;; RCS: $Id$
;; Keywords: OO, lisp
;; This program is free software; you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation; either version 2, or (at your option)
;; any later version.
;; This program is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; GNU General Public License for more details.
;; You should have received a copy of the GNU General Public License
;; along with this program; if not, you can either send email to this
;; program's author (see below) or write to:
;;              The Free Software Foundation, Inc.
;;              675 Mass Ave.
;;              Cambridge, MA 02139, USA.
;; Please send bug reports, etc. to

;;; Commentary:
;; Base classes for EIEIO.  These classes perform some basic tasks
;; but are generally useless on their own.  To use any of these classes,
;; inherit from one or more of them.

(require 'eieio)

;;; Code:
;;; eieio-instance-inheritor
;; Enable instance inheritance via the `clone' method.
;; Works by using the `slot-unbound' method which usually throws an
;; error if a slot is unbound.
(defclass eieio-instance-inheritor ()
  ((parent-instance :initarg :parent-instance
		    :type eieio-instance-inheritor-child
		    "The parent of this instance.
If a slot of this class is reference, and is unbound, then  the parent
is checked for a value.")
  "This special class can enable instance inheritance.
Use `clone' to make a new object that does instance inheritance from
a parent instance.  When a slot in the child is referenced, and has
not been set, use values from the parent."
  :abstract t)

(defmethod slot-unbound ((object eieio-instance-inheritor) class slot-name fn)
  "If a slot OBJECT in this CLASS is unbound, try to inherit, or throw a signal.
SLOT-NAME, is the offending slot.  FN is the function signalling the error."
  (if (slot-boundp object 'parent-instance)
      (eieio-oref (oref object parent-instance) slot-name)

(defmethod clone ((obj eieio-instance-inheritor) &rest params)
  "Clone OBJ, initializing `:parent' to OBJ.
All slots are unbound, except those initialized with PARAMS."
  (let ((nobj (make-vector (length obj) eieio-unbound))
	(nm (aref obj object-name))
	(passname (and params (stringp (car params))))
	(num 1))
    (aset nobj 0 'object)
    (aset nobj object-class (aref obj object-class))
    ;; The following was copied from the default clone.
    (if (not passname)
	  (if (string-match "-\\([0-9]+\\)" nm)
	      (setq num (1+ (string-to-int (match-string 1 nm)))
		    nm (substring nm 0 (match-beginning 0))))
	  (aset nobj object-name (concat nm "-" (int-to-string num))))
      (aset nobj object-name (car params)))
    ;; Now initialize from params.
    (if params (shared-initialize nobj (if passname (cdr params) params)))
    (oset nobj parent-instance obj)

;;; eieio-instance-tracker
;; Track all created instances of this class.
;; The class must initialize the `tracking-symbol' slot, and that
;; symbol is then used to contain these objects.
(defclass eieio-instance-tracker ()
  ((tracking-symbol :type symbol
		    :allocation :class
		    "The symbol used to maintain a list of our instances.
The instance list is treated as a variable, with new instances added to it.")
  "This special class enables instance tracking.
Inheritors from this class must overload `tracking-symbol' which is
a variable symbol used to store a list of all instances."
  :abstract t)

(defmethod initialize-instance :AFTER ((this eieio-instance-tracker)
				       &rest fields)
  "Make sure THIS is in our master list of this class.
Optional argument FIELDS are the initialization arguments."
  ;; Theoretically, this is never called twice for a given instance.
  (let ((sym (oref this tracking-symbol)))
    (if (not (member this (symbol-value sym)))
	(set sym (append (symbol-value sym) (list this))))))

(defmethod delete-instance ((this eieio-instance-tracker))
  "Remove THIS from the master list of this class."
  (set (oref this tracking-symbol)
       (delq this (symbol-value (oref this tracking-symbol)))))

;; In retrospect, this is a silly function.
(defun eieio-instance-tracker-find (key field list-symbol)
  "Find KEY as an element of FIELD in the objects in LIST-SYMBOL.
Returns the first match."
  (object-assoc key field (symbol-value list-symbol)))

;;; eieio-singleton
;; The singleton Design Pattern specifies that there is but one object
;; of a given class ever created.  The EIEIO singleton base class defines
;; a CLASS allocated slot which contains the instance used.  All calls to
;; `make-instance' will either create a new instance and store it in this
;; slot, or it will just return what is there.
(defclass eieio-singleton ()
  ((singleton :type eieio-singleton
	      :allocation :class
	      "The only instance of this class that will be instantiated.
Multiple calls to `make-instance' will return this object."))
  "This special class causes subclasses to be singletons.
A singleton is a class which will only ever have one instace."
  :abstract t)

(defmethod constructor :STATIC ((class eieio-singleton) name &rest fields)
  "Constructor for singleton CLASS.
NAME and FIELDS initialize the new object.
This constructor guarantees that no matter how many you request,
only one object ever exists."
  (let ((old (oref-default class singleton)))
    (or old (call-next-method))))

;;; eieio-persistent
;; For objects which must save themselves to disk.  Provides a
;; `object-save' method to save an object to disk, and a
;; `eieio-persistent-read' function to call to read an object
;; from disk.
;; Also provide the method `eieio-persistent-path-relative' to
;; calculate path names relative to a given instance.  This will
;; can make the saved object location independent of all file
;; references are made relative.
(defclass eieio-persistent ()
  ((file :initarg :file
	 :type string
	 "The save file for this persistent object.
This must be a string, and must be specified when the new object is
   (extension :type string
	      :allocation :class
	      :initform ".eieio"
	      "Extension of files saved by this object.
Enables auto-choosing nice file names based on name.")
   (file-header-line :type string
		     :allocation :class
		     :initform ";; EIEIO PERSISTENT OBJECT"
		     "Header line for the save file.
This is used with the `object-write' method."))
  "This special class enables persistence through save files
Use the `object-save' method to write this object to disk.  The save
format is Emacs Lisp code which calls the constructor for the saved
object.  For this reason, only slots which do not have an `:initarg'
specified will not be saved."
  :abstract t)

(defmethod eieio-persistent-save-interactive ((this eieio-persistent) prompt
					      &optional name)
  "Perpare to save THIS.  Use in an `interactive' statement.
Query user for file name with PROMPT if THIS does not yet specify
a file.  Optional argument NAME specifies a default file name."
  (unless (slot-boundp this 'file)
      (oset this file
	    (read-file-name prompt nil
			    (if   name
				(concat name (oref this extension))
  (oref this file))

(defun eieio-persistent-read (filename)
  "Read a persistent object from FILENAME."
    (let ((ret nil))
      (set-buffer (get-buffer-create " *tmp eieio read*"))
	    (insert-file filename)
	    (goto-char (point-min))
	    (setq ret (read (current-buffer)))
	    (if (not (child-of-class-p (car ret) 'eieio-persistent))
		(error "Corrupt object on disk"))
	    (setq ret (eval ret))
	    (oset ret file filename))
	(kill-buffer " *tmp eieio read*"))

(defmethod object-write ((this eieio-persistent) &optional comment)
  "Write persistent object THIS out to the current stream.
Optional argument COMMENT is a header line comment."
  (call-next-method this (or comment (oref this file-header-line))))

(defmethod eieio-persistent-path-relative ((this eieio-persistent) file)
  "For object THIS, make absolute file name FILE relative."
  ;; Woah!  Look at `file-relative-name' as a solution.
  (file-relative-name (expand-file-name file)
		      (file-name-directory (oref this file))))

(defmethod eieio-persistent-save ((this eieio-persistent) &optional file)
  "Save persistent object THIS to disk.
Optional argument FILE overrides the file name specified in the object
    (let ((b (set-buffer (get-buffer-create " *tmp object write*")))
	  (default-directory (file-name-directory (oref this file)))
	  (cfn (oref this file)))
	    (let ((standard-output (current-buffer)))
	      (oset this file
		    (if file
			(eieio-persistent-path-relative this file)
		      (file-name-nondirectory cfn)))
	      (object-write this (oref this file-header-line)))
	    (write-file cfn nil))
	;; Restore :file, and kill the tmp buffer
	(oset this file cfn)
	(setq buffer-file-name nil)
	(kill-buffer b)))))

;; Notes on the persistent object:
;; It should also set up some hooks to help it keep itself up to date.

;;; Named object
;; Named objects use the objects `name' as a slot, and that slot
;; is accessed with the `object-name' symbol.

(defclass eieio-named ()
  "Object with a name.
Name storage already occurs in an object.  This object provides get/set
access to it."
  :abstract t)

(defmethod slot-missing ((obj eieio-named)
			 slot-name operation &optional new-value)
  "Called when a on-existant slot is accessed.
For variable `eieio-named', provide an imaginary `object-nam' slot.
Argument OBJ is the Named object.
Argument SLOT-NAME is the slot that was attempted to be accessed.
OPERATION is the type of access, such as `oref' or `oset'.
NEW-VALUE is the value that was being set into SLOT if OPERATION were
a set type."
  (if (or (eq slot-name 'object-name)
	  (eq slot-name :object-name))
      (cond ((eq operation 'oset)
	     (if (not (stringp new-value))
		 (signal 'invalid-slot-type
			 (list obj slot-name 'string new-value)))
	     (object-set-name-string obj new-value))
	    (t (object-name-string obj)))

(provide 'eieio-base)

;;; eieio-base.el ends here