CODEWITHSUNDEEP
clojurenull
Attilio
Attilio

Reputation: 1722

fnil-like function in Clojure for defining output

In Clojure, the fnil function can be used to wrap another function: if the argument of the wrapped function would be nil, the wrapper will change it to something else.

E.g. ((fnil * 0) nil) ; returns 0 However (* nil 0) would throw an NPE.

What I'm asking is if there is a similar, built-in function that modifies the output, in case the input is nil. (In other words, it does not even call the wrapped function, it just returns the default value instead.)

In other words, is there a built-in function equivalent to the following?

(defn ifnil [fun default]
      (fn [& args]
          (if (some nil? args) default (apply fun args))))


; ((ifnil * nil) 1 2 3) ; returns 6
; ((ifnil * nil) 1 nil 3) ; returns nil

N.B.: As always, "no, there is no such function" is also a valid answer (which I suspect, btw.)

Upvotes: 2

Views: 355

Answers (1)

Ivan Grishaev
Ivan Grishaev

Reputation: 1681

There is no such a function, as far as I know. Your implementation looks well, so why not to use it in your code.

What may be improved here is a better name of the function: ifnil might be a bit confusing for your teammates or those who will support your code.

Also, you said in case the input is nil. But in your code, you check for at least one argument is nil. That differs slightly.

And one more thing, personally I'm not a fan of failing to defaults silently. Maybe, you'd better to validate the input data either manually or using schema/spec and write logs. Because fnil mostly used for non-existing keys with update/update-in. But you function tends to be rather a validator.

Upvotes: 1

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