Sorry, I've misread your post. If you want this feature to be added to
Clojure, please submit a ticket at http://dev.clojure.org/jira/browse/CLJ
JW
On Thu, Jan 30, 2014 at 3:16 PM, pron <ron.press...@gmail.com> wrote:
> I'm not caching the values, only the mapping from keywords to methods (the
> caching is per class, not per bean). It's just saving the
> introspection/reflection on each call. The values themselves are always
> obtained directly from the bean.
>
>
> On Thursday, January 30, 2014 4:12:31 PM UTC+2, Jozef Wagner wrote:
>
>> Hi,
>>
>> Not every bean is immutable, so you cannot cache its values by default.
>> If reading from the bean is expensive for you, either create a normal
>> hash-map with into {} and select-keys, or use memoize.
>>
>> user=> (def b (bean (java.util.Date.)))
>> #'user/b
>> user=> (def hm (into {} (select-keys b [:year :month :date])))
>> #'user/hm
>> user=> hm
>> {:date 30, :month 0, :year 114}
>> user=> (def mb (memoize b))
>> #'user/mb
>> user=> (mb :day)
>> 4
>>
>> JW
>>
>>
>>
>> On Thu, Jan 30, 2014 at 2:35 PM, pron <ron.pr...@gmail.com> wrote:
>>
>>> The bean function is a very useful Java interop feature that provides
>>> a read-only view of a Java Bean as a Clojure map.
>>> As it stands, the function performs introspection on the bean's class
>>> whenever the function is called:
>>>
>>>
>>>
>>> (defn bean
>>> "Takes a Java object and returns a read-only implementation of the
>>>
>>>
>>> map abstraction based upon its JavaBean properties."
>>> {:added "1.0"}
>>>
>>>
>>> [^Object x]
>>> (let [c (. x (getClass))
>>>
>>>
>>> pmap (reduce1 (fn [m ^java.beans.PropertyDescriptor pd]
>>>
>>>
>>> (let [name (. pd (getName))
>>>
>>>
>>> method (. pd (getReadMethod))]
>>>
>>>
>>> (if (and method (zero? (alength (. method
>>> (getParameterTypes)))))
>>>
>>>
>>> (assoc m (keyword name) (fn []
>>> (clojure.lang.Reflector/prepRet (.getPropertyType pd) (. method (invoke x
>>> nil)))))
>>>
>>>
>>> m)))
>>> {}
>>> (seq (.. java.beans.Introspector
>>>
>>>
>>> (getBeanInfo c)
>>>
>>>
>>>
>>> (getPropertyDescriptors))))
>>> v (fn [k] ((pmap k)))
>>>
>>>
>>> snapshot (fn []
>>> (reduce1 (fn [m e]
>>>
>>>
>>> (assoc m (key e) ((val e))))
>>>
>>>
>>> {} (seq pmap)))]
>>>
>>>
>>>
>>> (proxy [clojure.lang.APersistentMap]
>>> []
>>>
>>>
>>> (containsKey [k] (contains? pmap k))
>>>
>>>
>>> (entryAt [k] (when (contains? pmap k) (new clojure.lang.MapEntry k (v
>>> k))))
>>>
>>>
>>> (valAt ([k] (when (contains? pmap k) (v k)))
>>>
>>>
>>> ([k default] (if (contains? pmap k) (v k) default)))
>>>
>>>
>>> (cons [m] (conj (snapshot) m))
>>>
>>>
>>> (count [] (count pmap))
>>>
>>>
>>> (assoc [k v] (assoc (snapshot) k v))
>>>
>>>
>>> (without [k] (dissoc (snapshot) k))
>>>
>>>
>>> (seq [] ((fn thisfn [plseq]
>>>
>>>
>>> (lazy-seq
>>> (when-let [pseq (seq plseq)]
>>>
>>>
>>> (cons (new clojure.lang.MapEntry (first pseq) (v
>>> (first pseq)))
>>>
>>>
>>> (thisfn (rest pseq)))))) (keys pmap))))))
>>>
>>>
>>>
>>>
>>>
>>> I propose to cache the pmap value for each class using JDK 7's
>>> ClassValue <http://docs.oracle.com/javase/7/docs/api/>. Here's a
>>> proposed implementation:
>>>
>>> (def ^:private ^java.lang.ClassValue bean-class-value
>>>
>>>
>>> (proxy [java.lang.ClassValue]
>>> []
>>> (computeValue [c]
>>>
>>>
>>> (reduce (fn [m ^java.beans.PropertyDescriptor pd]
>>>
>>>
>>> (let [name (. pd (getName))
>>>
>>>
>>> method (. pd (getReadMethod))
>>>
>>>
>>> type (.getPropertyType pd)]
>>> (if (and method (zero? (alength (. method
>>> (getParameterTypes)))))
>>>
>>>
>>> (assoc m (keyword name) (fn [x]
>>> (clojure.lang.Reflector/prepRet type (. method (invoke x nil)))))
>>>
>>>
>>> m)))
>>> {}
>>> (seq (.. java.beans.Introspector
>>>
>>>
>>> (getBeanInfo c)
>>> (getPropertyDescriptors)))))))
>>>
>>>
>>>
>>> (defn bean
>>> "Takes a Java object and returns a read-only implementation of the
>>>
>>>
>>> map abstraction based upon its JavaBean properties."
>>> {:added "1.0"}
>>>
>>>
>>> [^Object x]
>>> (let [c (. x (getClass))
>>>
>>>
>>> pmap (.get bean-class-value c)
>>>
>>>
>>> v (fn [k] ((pmap k) x))
>>>
>>>
>>> snapshot (fn []
>>> (reduce (fn [m e]
>>>
>>>
>>> (assoc m (key e) ((val e) x)))
>>>
>>>
>>> {} (seq pmap)))]
>>> (proxy [clojure.lang.APersistentMap]
>>>
>>>
>>> []
>>> (containsKey [k] (contains? pmap k))
>>>
>>>
>>> (entryAt [k] (when (contains? pmap k) (new clojure.lang.MapEntry k (v
>>> k))))
>>>
>>>
>>> (valAt ([k] (when (contains? pmap k) (v k)))
>>>
>>>
>>> ([k default] (if (contains? pmap k) (v k) default)))
>>>
>>>
>>> (cons [m] (conj (snapshot) m))
>>>
>>>
>>> (count [] (count pmap))
>>> (assoc [k v] (assoc (snapshot) k v))
>>>
>>>
>>> (without [k] (dissoc (snapshot) k))
>>>
>>>
>>> (seq [] ((fn thisfn [plseq]
>>>
>>>
>>> (lazy-seq
>>> (when-let [pseq (seq plseq)]
>>>
>>>
>>> (cons (new clojure.lang.MapEntry (first pseq) (v
>>> (first pseq)))
>>>
>>>
>>> (thisfn (rest pseq)))))) (keys pmap))))))
>>>
>>>
>>>
>>>
>>>
>>>
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