Personally, I don't use this particular style for.. probably pretty poor
reasons. I find that I end up declaring every constant that might be needed in
a file in a single let at the top of the file because:
a) Clojure's declare before use semantics make ordering technically important
rather than simply a matter of aesthetic or conceptual grouping.
b) If I have several constants, trying to scope them only to the functions that
use them isn't easy/always possible.
c) I have assumed ( based on no evidence ) that Clojure would be lazy enough to
defer initialisation of def'd items until they were used, but a top level let
would always have to be executed at file load time.
d) I find that indenting almost the whole file because it is inside the let..
displeasing. But not indenting it is worse. I'm a bit neurotic about layout.
if you think it is a good practice, I might well have another try at it and see
if I can make peace with it.
R.
On 18 Sep 2011, at 22:08, Alan Malloy wrote:
> What really puzzles me is that it doesn't seem to be generally
> regarded as idiomatic Clojure style to just use top-level (let)s for
> your "private" globals. This has lots of benefits:
>
> - If you do this you can make them actually, genuinely private, rather
> than just marked as "please don't use this"
> - You get more self-documenting source code: (let [x 1] (defn foo []
> (...use x...))) is clear about how and where x will be used, while
> (def- x 1) (defn foo [] (...use x...)) leaves open the possibility
> that x is important all over the namespace.
> - You avoid runtime var-deref costs for constants that will never
> change.
>
> I find this style so useful and readable that I'm curious why it isn't
> more popular in the community at large.
>
> On Sep 18, 2:14 am, Rob Lally <rob.la...@gmail.com> wrote:
>> Thanks for the reference Mark, much appreciated.
>>
>> I add the private meta-data by hand, but (defn- foo 2) is so much more
>> succinct than (def ^:private foo 2) - where ^:private is almost half the
>> declaration. I also find the placement of the meta-data tag to be intrusive
>> and disruptive when reading... but that's just a personal peccadillo.
>>
>> I find your comments that you don't feel as much need to mark defs as
>> private as often as defns really interesting, because it is quite different
>> to my own practice. I tend to look at ^:private primarily as a way to inform
>> users of a namespace that this def is something they can safely ignore
>> because it is an implementation detail; you only need to pay attention to
>> this if you're going to modify the code.
>>
>> I've spent 5 mins looking at random source files from a few clojure projects
>> and I seem to use more defs than most people. I tend to pull out a fairly
>> high percentage of literals into expanatory defs, whereas the small sample
>> of files that I trolled through seemed to have a different feel for the
>> tipping point when a def is appropriate.
>>
>> I am surprised at other comments in this chain where people would rather see
>> the removal of def- than the addition of additional variants of def
>> derivatives. I'm not arguing that I'm right, or that things should change,
>> but personally I feel that controlling the exposed surface area of an API is
>> crucial to comprehensibility and maintainability, and that making
>> minimisation of surface area as trivial as possible will benefit us all.
>>
>> Thanks to everyone for taking the time to write down their thoughts,
>>
>> R.
>>
>> On 17 Sep 2011, at 16:37, Mark Rathwell wrote:
>>
>>> A previous discussion on the topic can be found here [1]. You can
>>> easily add the private metadata yourself:
>>
>>> Clojure 1.2: (def ^{:private true} size 25)
>>> Clojure 1.3: (def ^:private size 25)
>>
>>> I think probably the reason against it is that generally there is not
>>> as much reason to use a constant, for example, outside of its
>>> namespace as there is with functions, and therefore more need for
>>> marking functions meant only for internal use as such (but that is
>>> just guessing at other peoples' thought processes).
>>
>>> [1]http://groups.google.com/group/clojure/browse_thread/thread/80d873ef6...
>>
>>> On Sat, Sep 17, 2011 at 10:54 AM, Rob Lally <rob.la...@gmail.com> wrote:
>>>> Hi all,
>>
>>>> Whilst trying to minimise the visible surface areas of namespaces, I've
>>>> often felt the need for a def- function/macro that marks a def'ed var with
>>>> :private metadata. An analog of defn-, if you will.
>>
>>>> Is there a reason that I shouldn't do this or a reason that it doesn't
>>>> seem to be a member of the core lib?
>>
>>>> In the spirit of Hunt & Thomas' "Select isn't broken", when I encounter
>>>> something this trivial, useful and absent I tend to conclude that I'm the
>>>> one who's got things wrong.
>>
>>>> Thanks in advance,
>
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