On Sep 24, 10:59 am, Miron Brezuleanu <[email protected]> wrote:
> Well, I only want to enforce duck-typing :-) - for instance, make sure
> via unit tests that a function that should return a data structure
> with certain properties always returns such a data structure.
Not exactly what you asked for, but I added a defstruct* helper to my
utils.clj. I'm still not entirely sure it's a good idea, but here it
is:
(defmacro defstruct*
"Wrapper for defstruct which also creates a simple duck type
checking
function."
[name & slots]
`(do
(defstruct ~name ~...@slots)
(defn ~(symbol (str "is-" name "?")) [x#]
(if (map? x#)
(let [sample# (struct ~name)]
(empty? (clojure.set/difference
(set (keys sample#)) (set (keys x#)))))
false))))
Use it just like you use defstruct, e.g.: (defstruct* person :first-
name :last-name :age), but it will also create a little type-checker
function: is-person? Here are some tests to see how it works:
(defstruct* duck-typed-struct :a :b :c)
(deftest duck-typed-predicates
(let [dt1 (struct duck-typed-struct 1 2 3)
dt2 {:a 4 :b 5 :c 6}
dt3 (struct duck-typed-struct 1 2)
dt4 {:a 4 :b 5 :c nil}
not-dt1 {:a 4 :b 5}
not-dt2 {:d 7 :e 8}
not-dt3 {:a 4 :b 5 :d 7}]
(is (is-duck-typed-struct? dt1))
(is (is-duck-typed-struct? dt2))
(is (is-duck-typed-struct? dt3))
(is (is-duck-typed-struct? dt4))
(is (not (is-duck-typed-struct? not-dt1)))
(is (not (is-duck-typed-struct? not-dt2)))
(is (not (is-duck-typed-struct? not-dt3)))))
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