Property Lists Outside Symbols

The following functions can be used to manipulate property lists. They all default to comparing property names using eq.

Function: plist-get plist property &optional predicate

This returns the value of the property property stored in the property list plist. Comparisons are done with predicate, which defaults to eq. It accepts a malformed plist argument. If property is not found in the plist, it returns nil. For example,

(plist-get '(foo 4) 'foo)
     ⇒ 4
(plist-get '(foo 4 bad) 'foo)
     ⇒ 4
(plist-get '(foo 4 bad) 'bad)
     ⇒ nil
(plist-get '(foo 4 bad) 'bar)
     ⇒ nil

Function: plist-put plist property value &optional predicate

This stores value as the value of the property property in the property list plist. Comparisons are done with predicate, which defaults to eq. It may modify plist destructively, or it may construct a new list structure without altering the old. The function returns the modified property list, so you can store that back in the place where you got plist. For example,

(setq my-plist (list 'bar t 'foo 4))
     ⇒ (bar t foo 4)
(setq my-plist (plist-put my-plist 'foo 69))
     ⇒ (bar t foo 69)
(setq my-plist (plist-put my-plist 'quux '(a)))
     ⇒ (bar t foo 69 quux (a))

Function: lax-plist-get plist property

This obsolete function is like plist-get except that it compares properties using equal instead of eq.

Function: lax-plist-put plist property value

This obsolete function is like plist-put except that it compares properties using equal instead of eq.

Function: plist-member plist property &optional predicate

This returns non-nil if plist contains the given property. Comparisons are done with predicate, which defaults to eq. 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 property.