Question

I’m writing a small application that includes a password change function with validators for password quality. Currently the validators are specified in a map like so:

(def validations
  {:min-length 6
   :max-length 32})

The validations map is defined in the validations namespace, but I plan to move it to a configuration namespace later on. My decision to use a map in this way was to make configuration straight-forward for non-programmers.

There are a number of validation functions in the validations namespace that usually take the form:

(defn min-length [n s]
  {:req (str "be at least " n " characters long")
   :pass? (>= (.length (or s "")) n)})

So with the function above (min-length 3 "clojure") would return {:req "be at least 3 characters long", :pass? true}.

I can validate a password with this function in the validation namespace with this function:

(defn validate-new-password [password]
  (into {} (for [[k v] validations]
             [k (eval (list (-> k name symbol) v password))])))

The result being something like:

>(validate-new-password "clojure")
{:min-length {:req "be at least 6 characters long", :pass? true}, 
 :max-length {:req "be no longer than 32 characters long", :pass? true}, 
 :min-digits {:req "have at least 1 digit", :pass? false},  
 :allow-whitespace {:req "not contain spaces or tabs", :pass? true}, 
 :allow-dict-words {:req "not be a dictionary word", :pass? false}}

What is the most practical way to resolve the validation functions when the validate-new-password function is called from outside the validation namespace?

I’ve tried a number of approaches over the past weeks but I’ve never been happy with the resulting form (and none of them have worked!).

Generally I guess the question is “how are symbols in a :require’d namespace resolved when called by functions within that namespace?”

I’m also interested on any general comments about my implementation.

Answer 1

There is no need for eval, as in 98% of the cases.

(defn validate-new-password
  [password]
  (into {} (for [[k v] validations]
             [k ((->> k name (symbol "your.name.space") resolve) v password)])))