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access

This library brings a helper to access nested data structures.

It has a fairly detailed readme with examples.

I’ve prepared one example for you:

POFTHEDAY> (defparameter obj
               (make-instance 'foo
                              :bar (make-hash-table)))

;; Now we will access a slot 'bar inside the object:
POFTHEDAY> (access:accesses *obj* 'bar)
#<HASH-TABLE :TEST EQL :COUNT 0 {1007D39263}>

;; Now we go deeper and access an item :some
;; inside this hash-table:
POFTHEDAY> (access:accesses *obj* 'bar :some)
NIL

;; Accessor is allow us to use setf and it will automatically
;; create all intermediate nodes:
POFTHEDAY> (setf (access:accesses *obj* 'bar :some)
                 "Hello world")
"Hello world"

;; Here is our result:
POFTHEDAY> (access:accesses *obj* 'bar :some)
"Hello world"

POFTHEDAY> (loop for key being the hash-keys in (get-bar *obj*)
                   using (hash-value value)
                 collect (cons key value))
((:SOME . "Hello world"))

It is able to access CLOS slots, plists, array items, hash keys, etc.

Also, ‘access’ supports a reader syntax with a dotted notation, but I prefer to use a shorter macro ->:

(defmacro -> (obj &rest path)
  `(access:accesses ,obj ,@path))

;; Somewhere in the code:

(defcached get-stock-name (ticker)
  (-> (%get-stock-data ticker)
      :|payload|
      :|symbol|
      :|showName|))

Usually, I use ‘access’ to process plists results from a Jonathan - JSON parser. But it should be very convenient for accessing other data structures too.