On Sep 10, 11:33 am, "Michael Reid" <[EMAIL PROTECTED]> wrote:
> Hi folks,
>
> There was a thread a little while back
> (http://groups.google.com/group/clojure/browse_thread/thread/8c4bea212...)
> about implementing true data hiding by nesting defns under a let,
> e.g.:
>
> (let [hidden-ref (ref 10)]
> (defn get-secret [] @hidden-ref))
>
> This was mentioned to be bad style. If this is the general consensus,
> what suggestions do you have if you want to write a macro which
> generates a Java class using (genclass) and also generates default
> implementations for some getter and setter methods?
>
> For example, I want to write a macro that transforms:
>
> (defbean MyBean :myint 0, :mystring "default")
>
> into something like:
>
> (gen-and-load-class "MyBean" ...)
>
> (defn MyBean-getMyint [this] ...)
> (defn MyBean-setMyInt [this value] ...)
> (defn MyBean-getMystring [this] ...)
> (defn MyBean-setMystring [this value] ...)
>
> However, in order to do this, the macro needs to expand to something like:
> (do
> (gen-and-load-class "MyBean" ...)
>
> (defn MyBean-getMyint [this] ...)
> (defn MyBean-setMyInt [this value] ...)
> (defn MyBean-getMystring [this] ...)
> (defn MyBean-setMystring [this value] ...))
>
> In my case I've been wrapping this in a (let) as there are some locals
> that I need to setup in order to fill in the templates for the getters
> and setters.
>
> I'm wondering if there is a different way, in light of the dislike for
> placing (defn) in a nested structure instead of the top-level.
>
> Thoughts?
>
There's nothing wrong with this. Any macro that needs to emit more
than one def is going to have to emit them in a do or let.
The general admonition against non-top-level defs is to guard against
their use as a form of assignment to global vars. From the docs
(http://clojure.org/special_forms) :
"Using def to modify the root value of a var at other than the top
level is usually an indication that you are using the var as a mutable
global, and is considered bad style."
That's not what you are doing. You are using def appropriately, which
is to _establish_ root bindings, not modify them.
Rich
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