James, are you saying that with such a core.typed annotation for function
available in that example, that it would give a warning if available or any
of the functions it calls accesses any keys other than :stock and :reserved
?
If so, that is quite impressive.
Andy
On Fri, May 8, 2015 at 10:36 AM, James Reeves <ja...@booleanknot.com> wrote:
> Avoiding encapsulation doesn't mean that every function needs to act on a
> huge global data structure. On the contrary, one of the core ideas of
> Clojure is that we should try to reduce incidental interconnections. What
> you describe in your example is essentially complexity creep.
>
> Ideally, functions should access only the data they need. For instance,
> you might have a function:
>
> (defn available [{:keys [stock reserved]}]
> (- stock reserved))
>
> In the function arguments we're deliberately restricting the data down to
> two keys. We could also use core.typed to enforce this for us:
>
> (ann available ['{:stock Int, :reserved Int} -> Int])
>
> - James
>
> On 8 May 2015 at 17:29, Brian Craft <craft.br...@gmail.com> wrote:
>
>> Talk on the list about encapsulation usually comes back to some variation
>> of "you don't need it when you have immutable data structures". But in the
>> long term I'm finding the problem of working w/o encapsulation is not the
>> danger of data being mutated under you. Rather, it's the danger of all the
>> module boundaries blurring over time, leading to the big ball of mud: a
>> very fragile code base where everything depends on everything else.
>>
>> E.g. if you model your application with a plain data structure which you
>> pass around to different modules, each concerned with a small part of that
>> data structure, the tendency over time is for every module to become
>> concerned with every part of that data structure. Then you have no
>> separation, nothing is reusable, and the code is very fragile.
>>
>> How do you avoid this, practically? In OO it would be enforced with
>> encapsulation, so the next developer (which might be me, six months later)
>> trying to fix a bug, or add a feature, knows "Oh, I shouldn't peek in here:
>> this module isn't supposed to depend on that piece of data".
>>
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