On Fri, May 20, 2011 at 2:24 PM, László Török <ltoro...@gmail.com> wrote:
> On May 20, 2011 7:55 PM, "Fogus" <mefo...@gmail.com> wrote:
>> In the alpha7 release the defrecord macro was changed to generate a
>> couple of auxiliary functions (for a record R) named map->R and ->R.
>> The first takes a map and returns a function of its contents. The
>> second takes the same number of arguments as the record constructor.
>> It's the definition of this second function that is reporting an
>> error. It's easy enough to fix, but I guess the question is should it
>> be fixed? That is, do people define records with 19+ fields? Does
>> this pose a problem for existing code?
> Hi,
>
> What's the incremental runtime cost of increasing the max number of fields
> to 40? :-)
Oh, there's no need for that. Just add a little smarts to the
constructor generating macro to detect 19+ fields and then define it
as
(defn ->Foo [& fields]
(if (not= (count fields) whatever)
(throw-arity-exception)
(Foo. (nth fields 0) (nth fields 1) (nth fields 2) ...)))
or maybe for efficiency use a let cascade:
(let [p1 (first fields)
fields (rest fields)
p2 (first fields)
fields (rest fields)
...]
...)
Of course there's probably some JVM limit on the number of constructor
args, too.
I'd suggest if you have records that large to consider restructuring
them to have a smaller number of fields that are more composite --
seqs, vectors, sets, maps, even nested records. Surely there's *some*
structure beyond a heterogeneous assortment of twenty-plus objects?
--
Protege: What is this seething mass of parentheses?!
Master: Your father's Lisp REPL. This is the language of a true
hacker. Not as clumsy or random as C++; a language for a more
civilized age.
--
You received this message because you are subscribed to the Google
Groups "Clojure" group.
To post to this group, send email to clojure@googlegroups.com
Note that posts from new members are moderated - please be patient with your
first post.
To unsubscribe from this group, send email to
clojure+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/clojure?hl=en
