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9.4.1 Accessing Symbol Properties

The following functions can be used to access symbol properties.

Function: get symbol property ¶

This function returns the value of the property named property in symbol’s property list. If there is no such property, it returns nil. Thus, there is no distinction between a value of nil and the absence of the property.

The name property is compared with the existing property names using eq, so any object is a legitimate property.

See put for an example.

Function: put symbol property value ¶

This function puts value onto symbol’s property list under the property name property, replacing any previous property value. The put function returns value.

(put 'fly 'verb 'transitive)
     ⇒'transitive
(put 'fly 'noun '(a buzzing little bug))
     ⇒ (a buzzing little bug)
(get 'fly 'verb)
     ⇒ transitive
(symbol-plist 'fly)
     ⇒ (verb transitive noun (a buzzing little bug))

Function: symbol-plist symbol ¶

This function returns the property list of symbol.

Function: setplist symbol plist ¶

This function sets symbol’s property list to plist. Normally, plist should be a well-formed property list, but this is not enforced. The return value is plist.

(setplist 'foo '(a 1 b (2 3) c nil))
     ⇒ (a 1 b (2 3) c nil)
(symbol-plist 'foo)
     ⇒ (a 1 b (2 3) c nil)

For symbols in special obarrays, which are not used for ordinary purposes, it may make sense to use the property list cell in a nonstandard fashion; in fact, the abbrev mechanism does so (see Abbrevs and Abbrev Expansion).

You could define put in terms of setplist and plist-put, as follows:

(defun put (symbol prop value)
  (setplist symbol
            (plist-put (symbol-plist symbol) prop value)))

Function: function-get symbol property &optional autoload ¶

This function is identical to get, except that if symbol is the name of a function alias, it looks in the property list of the symbol naming the actual function. See Defining Functions. If the optional argument autoload is non-nil, and symbol is auto-loaded, this function will try to autoload it, since autoloading might set property of symbol. If autoload is the symbol macro, only try autoloading if symbol is an auto-loaded macro.

Function: function-put function property value ¶

This function sets property of function to value. function should be a symbol. This function is preferred to calling put for setting properties of a function, because it will allow us some day to implement remapping of old properties to new ones.