OOP places a strong emphasis on information hiding, particularly by
wrapping data structures in APIs. Developers with a strong background in
OOP tend to try to replicate this style of programming in Clojure.
However, idiomatic Clojure emphasises exactly the opposite of this. In
Clojure, a bare data structure is generally preferable to one hidden behind
an API. In an OOP language, you typically start by considering your API,
but in Clojure, you start by considering how to structure your data.
This does mean doing without a safety net. In an OOP language, you can
perform some changes to the internal data structures without affecting the
API, but this comes at the price of repetition. Every time you create a new
data structure in an OOP language, you need to implement an API for it, but
if we discard the idea of information hiding, then we remove the need to
keep reinventing APIs.
- James
On 26 June 2014 02:34, Mark P <pierh...@gmail.com> wrote:
> I've only recently started real clojure development, so very much still
> learning what styles work and what don't. I have a question about naming
> attribute getters...
>
> Suppose I want to model "fruit" entities. I will use a hash-map to
> represent the data for each such entity, and will defn a "make" function to
> construct fruit instances. I will put "make" and any other fruit-related
> functions within a new namespace "myprog.fruit".
>
> Because my data representation is a map, strictly speaking I don't need
> any attribute getter functions. Because I could simply use the attribute
> keywords in the map as my getter functions, eg (:color fru). But I will
> create actual getter functions within my namespace anyway, for a few
> reasons.
>
> 1. It will signal to any users of my fruit library, which attributes
> are "official" and are expected to be used / supported, versus attributes
> which are more of an implementation detail.
> 2. Some attributes will simply be (defn color [fru] (:color fru)),
> whereas others are less direct, eg (defn red? [fru] (= :red fru)) or
> another eg (defn packingvol [{:keys [size]}] (* size size size)).
> 3. Down the track I can change my data representation, and just
> reimplement the getter functions. Users of my fruit library who have stuck
> to my getter functions interface will not need to change a thing.
>
> This approach seems okay to me so far, though I am open to critiques and
> alternative suggestions. But one issue has come to mind... leading to the
> question of this post...
>
> At the end of 2. above, I have defined a local let symbol "size" as part
> of the map destructuring. But it so happens I have already defined a size
> getter, namely (defn size [fru] (:size fru)). So within the definition of
> packingvol my size getter is masked by the local symbol "size". Now I'm
> not sure this masking causes much harm... I don't actually need to use the
> size getter here, and if I really needed it I could always use
> "myprog.fruit/size"... But something still makes me feel uncomfortable
> about it, maybe because this masking could end up happening a lot within my
> fruit.clj source code file.
>
> Now I could just switch to a new naming convention for my getters, ie
> "color-get", "red?-get", "size-get", "packingvol-get" etc. But I'm not
> sure I like the extra verbosity. And for users of my fruit library - who
> will be working in a different namespace - this problem mostly goes away as
> they will probably be namespace-qualifying access to my getters.
>
> Is using self-named attribute getters a good idea?
>
> Thanks,
>
> Mark.
>
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