I agree that you probably don't need to go overboard with hiding
stuff. For option 2 though there's no need for deftype. Just implement
the protocol with reifiy within the create function and use the
closure for state.
(defn create-woobly
[...]
(let [... put your queues and stuff here ...]
(reify Woobly
... implement protocol here ...)))
Dave
On Thu, May 9, 2013 at 9:15 AM, Gary Trakhman <gary.trakh...@gmail.com> wrote:
> If the interface provides everything that's needed, then there will be no
> need to dive in?
>
> I find attempts to hide that stuff frustrating when I'm a consumer of the
> code, if I need it, and I acknowledge that implementation details are
> subject-to-change when I take that risk, so only having something clearly
> marked off by documentation of intent would be what I would do as a producer
> of the code.
>
>
> On Thu, May 9, 2013 at 12:07 PM, Colin Yates <colin.ya...@gmail.com> wrote:
>>
>> (newbie, but trying hard!)
>>
>> I am designing a Woobly. A Woobly is non-trivial and has a number of
>> internal data structures (queues, worker threads etc.). You can 'add' and
>> 'remove' jobs from a Woobly.
>>
>> In OO land I might have a Woobly interface with the various methods which
>> provides a public API. I might also have a factory or more likely builder
>> somewhere which creates Wooblies.
>>
>> The part I am struggling with is how to create a Woobly without exposing
>> its internals. Let's imagine that Woobly uses an internal
>> LinkedBlockingQueue of a certain size.
>>
>> Option 1 - a big bag of data.
>> I could create a map of config/state/data that comprises the
>> implementation and have the creator function return that. Consumers can
>> then call other methods passing back that bag of config/state, but what
>> stops them simply diving into that bag themselves? For example:
>>
>> [code]
>> (defn create-woobly
>> ([] (create-woobly 100)
>> ([queue-size] {:queue (java.util.concurrent.LinkedBlockingQueue
>> queue-size)}))
>>
>> (defn add-job [woobly job] ....)
>>
>> ;; nothing stopping me diving into that state...
>> (.clear (:queue (create-wobbly)))
>> [/code]
>>
>> Option 2 - protocol and deftype
>> Alternatively I could implement an IWoobly protocol and create a single
>> deftype which is instantiated and returned from the 'create-woobly'
>> function? I am not sure I like this as it is really back to OO isn't it?
>>
>> I want to retain the notion of create returning a handle which is the
>> first argument in the other public functions, but the first way just feels
>> far too dangerous.
>>
>> Am I overthinking this - what do you all do to address this?
>>
>> Thanks a bunch.
>>
>> Col
>>
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