Elisp: Property List
What is Property List
Property list (in short, plist) is a list, but to be interpreted as list of pairs, like this:
'(key1 val1 key2 val2 …)
Property list is not supposed to have duplicate keys, and should always have even length.
Key should be lisp symbols, value can be any lisp object.
(info "(elisp) Property Lists")
Use of Property List
Property List is used as a simplest form of key/value pairs.
Property list is used extensively in emacs.
The 2 major use of property list are:
- Symbol's property list. Each symbol, is associated with a property list. Used primarily to store info related to the symbol, such as compiler info, but can be anything. [see Elisp: Symbol Property List]
- Text Properties. Any character or string in a buffer, can have a property list, used to store syntax color info, special keyboard shortcut, etc. [see Elisp: Text Properties]
Property list isn't a generic data structure. If you have more than 100 items, you probably should use Association List instead. [see Elisp: Association List]
Get a Key's Value
(plist-get PLIST PROP)
return the value of key PROP from property list PLIST. If key does not exist, return
nil. Existence of key is checked with
plist-get, but compare key using
(plist-get '(x 1 y 2) 'y) ; 2 (plist-get '(x 1 y 2) 'b) ; nil
(plist-put PLIST PROP VAL)
add or change the value of key PROP in PLIST to VAL. The new plist is returned. Use
(setq x (plist-put x prop val))to be sure to use the new value. Existence of key is checked with
plist-put, but compare key using
;; create a property list xx (setq xx '(a 1 b 2)) ;; set value to a existing key (setq xx (plist-put xx 'b 3)) xx ;; (a 1 b 3)
Check Key Existence
(plist-member PLIST PROP)
Return true if PLIST has the property PROP. . PROP is a symbol. Unlike
plist-get, this allows you to distinguish between a missing property and a property with the value
nil. The value is actually the tail of PLIST whose car is PROP.
(setq xx '(a 1 b 2)) ;; check if a key exist (plist-member xx 'b) ;; (b 2)
(info "(elisp) Plist Access")
Symbol's Property List
Each elisp symbol, can be attached a property list. Such is called “symbol plist”.
Elisp: Symbol Property List
Text in a buffer region can be attached a property list. Such is called “Text Properties”.
Elisp: Text Properties