Hello, Maybe you should consider creating a single function with 2 arities: with one argument, it's the getter, with two arguments, it's the setter (that returns the new type) !
(prop-foo obj) ; --> returns the property prop-foo (prop-foo obj newval) ; --> returns a new version of obj with prop-foo property set to newval Terse and uniform :-) ? 2009/4/26 David Nolen <dnolen.li...@gmail.com>: > You're right. The following includes code for handling this case via setin > and getin. I've also ditched macros, because that code couldn't support new > lexical scopes in the setter/getter definition. setin getin support works by > dynamically resolving getters and setters, thus this is slower than direct > access via assoc-in and get-in. > Personally I have to say now that this is written, I prefer the terseness > of: > (set-x some-map v) > over > (assoc some-map :x v) > This > (get-x some-map) > isn't as nice as > (:x map) > But it's also more explicit about how the map is being used- that a level > indirection is required because the implementation might change. > ;; ========================================== > (comment > (accessors x y z) > ; {:x 4} > (set-x {} 4) > (defset x [m v] > (assoc (assoc m :new "new") :x v)) > ;; {:new "new", :x {:y {:z 1}}} > (setin {:x {:y {:z 0}}} '(x y z) 1) > ;; 0 > (getin {:x {:y {:z 0}}} '(x y z)) > ; {:x 4, :new "new", :foo 9} > (let [z {:foo 9}] > (set-x z 4)) > ; 10 > (let [y {:z 10}] > (get-z y)) > ; [0 1 2] > (map get-x [{:x 0}, {:x 1}, {:x 2}])) > (defn setter* [sym] > `(defn ~(symbol (str "set-" sym)) [~'m ~'v] > (assoc ~'m ~(keyword (str sym)) ~'v))) > (defn getter* [sym] > `(defn ~(symbol (str "get-" sym)) [~'m] > (~(keyword (str sym)) ~'m))) > (defmacro defset [sym args & forms] > (let [set-sym (symbol (str "set-" sym))] > `(defn ~set-sym [...@args] > ~...@forms))) > (defmacro defget [sym args & forms] > (let [get-sym (symbol (str "get-" sym))] > `(defn ~get-sym [...@args] > ~...@forms))) > (defn find-accessor [sym acc-type] > (let [ns (or (namespace sym) > (str *ns*)) > sym-name (name sym)] > (find-var (symbol ns (str (name acc-type) "-" sym-name))))) > (defn setin [m [sym & syms] v] > (let [setter (find-accessor sym :set) > getter (find-accessor sym :get)] > (if syms > (setter m (set-in (getter m) syms v)) > (setter m v)))) > (defn getin [m [sym & syms]] > (let [getter (find-accessor sym :get)] > (if syms > (getin (getter m) syms) > (getter m)))) > (defmacro accessors [& syms] > `(do > ~@(map setter* syms) > ~@(map getter* syms))) > > On Sat, Apr 25, 2009 at 4:42 AM, MattH <mbhut...@gmail.com> wrote: >> >> It's worth considering how *nested* accessors would work in the >> context of immutability. >> >> The nested maps approach works really nicely, due in part to functions >> like assoc-in: >> >> ; From Mark Volkmann's tutorial >> (assoc-in person [:employer :address :city] "Clayton") >> >> What would the above update look like if 'address' was accessed using >> functions like get-address and set-address? >> >> Functions like assoc-in clearly rely on a uniform way of getting/ >> setting fields (i.e. maps). >> >> My *hunch* is that the right avenue is to extend/implement clojure's >> map classes if injecting behaviour is ever necessary. (A standard/ >> supported way to do this would be nice.) >> >> I'd be happy using constructor functions like (make-complex-number) >> and (make-person) which can hide detail of their implementations, but >> I'd also like to benefit from all that goes with the idiomatic use of >> maps. >> >> (My 2c) >> > > > > > --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en -~----------~----~----~----~------~----~------~--~---