"Meikel Brandmeyer" <m...@kotka.de> said:
> On May 31, 9:37 am, "Sina K. Heshmati" <s...@khakbaz.com> wrote:
>
>> The atomic 'state' doesn't seem to be visible to the datatype methods. The
>> question is why?
>>
>> (defprotocol prot-a
>> (op-a [self x y]))
>>
>> (let [state (atom 10)]
>> (deftype t-a [member]
>> prot-a
>> (op-a [self x y]
>> (+ (.member self) x y @state))))
>>
>> (def t-a-instance (t-a. 5))
>
> Of course not. deftype defines a type and not an environment. It's
> methods are not closures. (And even if they were, your state would be
> the same for all instances.) You have to pass the state as an argument
> to the constructor.
Now it makes more sense. Thanks.
> (defprotocol prot-a ...)
> (deftype t-a [state member] ...)
>
> (defn make-t-a [member] (t-a. (atom 0) member))
>
> (def t-a-instance (make-t-a 5))
I'll pass.
> If you actually want the same state for instances, use a private var.
>
> (defprotocol prot-a ...)
> (def ^{:private true} state (atom 0))
> (deftype t-a [member] ...)
>
> (def t-a-instance (t-a. 5))
This is a pretty solution but I tested it and it doesn't work the way it
should. That is, when I load [1] in a separate REPL, I can still see and
(reset!) the allegedly private 'state'.
user=> (load-file "path/tp/datatype-01.clj")
#'foo.datatype-01/t-a-instance
user=> (ns PREFIX.datatype-01)
nil
foo.datatype-01 => (op-a t-a-instance 1 2)
18
foo.datatype-01 => state
#<a...@302e67: 10>
foo.datatype-01 => @state
10
foo.datatype-01 => (reset! state 13)
13
foo.datatype-01 => @state
13
Kind regards,
SinDoc
[1]
http://github.com/sindoc/algorithms/blob/master/src/main/clojure/whiteboard/y2010/hide-adt-state/datatype-01.clj
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