Metrics

metrics/fn-length

Enabled by default	Version Added	Version Updated
false	1.6.0	1.6.0

Avoid defn-defined functions longer than some number (10) of lines of code. Longer functions are harder to read and should be split into smaller-purpose functions that are composed.

The total length is configurable, and the size can be configured (:body or :defn styles) to be measured from the entire defn form or the vector+body.

Examples

;; :body style (default)
(defn foo
  [arg] ;; <- starts here
  0
  1
  ...
  9
  10) ;; <- ends here

(defn foo
  ([] (foo 100)) ;; <- starts and ends here
  ([arg] ;; <- starts here
   0
   1
   ...
   9
   10)) ;; <- ends here

;; :defn style
(defn foo ;; <- starts here
  [arg]
  0
  1
  ...
  9
  10) ;; <- ends here

(defn foo ;; <- starts here
  ([] (foo 100))
  ([arg]
   0
   1
   ...
   9
   10)
) ;; <- ends here

Configurable Attributes

Name	Default	Options
:chosen-style	:body	:body, :defn
:length	10	Number

Reference

• https://guide.clojure.style/#function-length

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metrics/parameter-count

Enabled by default	Version Added	Version Updated
false	1.7.0	1.7.0

Avoid parameter lists with more than 4 positional parameters.

The number of parameters can be configured with :count. The default style :positional excludes & args rest parameters, and the style :include-rest includes them.

Functions with multiple arities will have each arity checked.

Examples

;; :positional style (default)
# bad
(defn example [a b c d e] ...)
(defn example ([a b c d e] ...) ([a b c d e f g] ...))
(defn example [a b c d e & args] ...)

# good
(defn example [a b c d] ...)
(defn example ([a b c] ...) ([a b c e] ...))
(defn example [a b c d & args] ...)

;; :include-rest style
# bad
(defn example [a b c d & args] ...)

# good
(defn example [a b c & args] ...)

Configurable Attributes

Name	Default	Options
:chosen-style	:positional	:positional, :include-rest
:count	4	Number

Reference

• https://guide.clojure.style/#function-positional-parameter-limit