aaa ok I see what you mean...well, yes everything starting with def can
be considered a 'global' var or even better a namespaced var (not really
a variable in the traditional sense)...In Noir's case most of the atoms
are maps so it could be that each Noir app registers its specific routes
on a specific key in the map...wildly guessing here...perhaps someone
else can provide more details...
In general however, this is how you would model small pieces of state in
Clojure...for example, designing a gui includes a lot of state
usually...so for example in most of my guis i have an atom at the top
which holds a map with all he stateful aspects of the gui...but you're
right - it's generally best to limit the amount of state in your program...
Jim
ps: defonce is not really related with singletons...there was a
clojure.contrib ns for singletons wasn't there?
On 12/09/12 15:54, the80srobot wrote:
Sorry I wasn't more clear - I'm not talking about defonce, but about
having refs (atoms) defined at the top level. When they're defined
like this, they basically become global variables, don't they? Having
two Noir apps would then mean they share the same routes, among other
things. Or am I missing something?
On Wednesday, September 12, 2012 4:49:34 PM UTC+2, Jim foo.bar wrote:
defonce simply means "do not bind the var if it already has a root
value"... I think it only applies when reloading your
namespace...to be
honest, I'm not sure why Chris has coded it like that (creating an
atom
is not really expensive), but i find it hard to believe that you
can' t
have 2 Noir apps on the same project...basically defonce it is the
same
as def unless there is already a root value for that var...
can anyone else add anything?
Jim
On 12/09/12 15:30, the80srobot wrote:
> Hello,
>
> So I've been working on a project at work, that required me to
code a
> simple web interface. I considered going with Noir, and while
reading
> the code, I noticed a pattern that seems to repeat throughout
most of
> the code that Chris Granger has published in Clojure. This is
what I'm
> referring to:
>
> ; these are at the top level in (ns noir.core)
> (defonce noir-routes (atom {}))
> (defonce route-funcs (atom {}))
> (defonce pre-routes (atom (sorted-map)))
> (defonce post-routes (atom []))
> (defonce compojure-routes (atom []))
>
> Now, I am new to Clojure, but I am not new to (functional)
programming
> and I'd like to think that I know a singleton when I see one. Is
that
> really what these are? If I'm right then defining your 'globals'
(for
> lack of a better word) like this would mean, among other things,
that
> you really can't have two independent Noir apps defined/running
in the
> same project - is that a correct assessment?
>
> Can someone more experienced shed some light on why it's done this
> way? My experience in functional programming has taught me to
always
> limit my scope - I would think that either using thread-local
bindings
> (and then rebinding them to child threads) or relying on lexical
scope
> would be preferable to polluting the global state. Is this a
Clojure
> best practice?
>
> Thanks. I'm looking to use Clojure a lot at work, and I'm trying to
> really understand the language before I throw it our production
problems.
>
> ~Adam
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