Style

style/apply-str

Enabled by default	Version Added	Version Updated
true	0.1	1.2.0

Check for round-about clojure.string/join.

Examples

; bad
(apply str x)

; good
(clojure.string/join x)

---

style/apply-str-interpose

Enabled by default	Version Added	Version Updated
true	0.1	1.2.0

Check for round-about clojure.string/join.

Examples

; bad
(apply str (interpose "," x))

; good
(clojure.string/join "," x)

---

style/apply-str-reverse

Enabled by default	Version Added	Version Updated
true	0.1	1.2.0

Check for round-about clojure.string/reverse.

Examples

; bad
(apply str (reverse x))

; good
(clojure.string/reverse x)

---

style/assoc-assoc

Enabled by default	Version Added	Version Updated
true	0.1	1.2.0

Layering assoc calls are hard to read. assoc-in is known and idiomatic.

Examples

; bad
(assoc coll :key1 (assoc (:key2 coll) :key2 new-val))
(assoc coll :key1 (assoc (coll :key2) :key2 new-val))
(assoc coll :key1 (assoc (get coll :key2) :key2 new-val))

; good
(assoc-in coll [:key1 :key2] new-val)

---

style/cond-else

Enabled by default	Version Added	Version Updated
true	0.1	0.1.85

It's nice when the default branch is consistent.

Examples

; bad
(cond
  (< 10 num) (println 10)
  (< 5 num) (println 5)
  true (println 0))

; good
(cond
  (< 10 num) (println 10)
  (< 5 num) (println 5)
  :else (println 0))

Reference

• https://guide.clojure.style/#else-keyword-in-cond

---

style/conj-vector

Enabled by default	Version Added	Version Updated
true	0.1	1.2.0

vector is succinct and meaningful.

Examples

; bad
(conj [] :a b {:c 1})

; good
(vector :a b {:c 1})

---

style/def-fn

Enabled by default	Version Added	Version Updated
true	1.0	1.0

(defn []) is preferable over (def (fn [])). Extrapolate to closures.

Examples

; bad
(def check-inclusion
  (let [allowed #{:a :b :c}]
    (fn [i] (contains? allowed i))))

; good
(let [allowed #{:a :b :c}]
  (defn check-inclusion [i]
    (contains? allowed i)))

; bad
(def some-func
  (fn [i] (+ i 100)))

; good
(defn some-func [i]
  (+ i 100))

---

style/eq-false

Enabled by default	Version Added	Version Updated
true	0.1	1.2.0

false? exists so use it.

Examples

; bad
(= false x)
(= x false)

; good
(false? x)

---

style/eq-nil

Enabled by default	Version Added	Version Updated
true	0.1	1.2.0

nil? exists so use it.

Examples

; bad
(= nil x)
(= x nil)

; good
(nil? x)

---

style/eq-true

Enabled by default	Version Added	Version Updated
true	0.1	1.2.0

true? exists so use it.

Examples

; bad
(= true x)
(= x true)

; good
(true? x)

---

style/eq-zero

Enabled by default	Version Added	Version Updated
true	0.1	1.2.0

zero? exists so use it.

Examples

; bad
(= 0 num)
(= num 0)
(== 0 num)
(== num 0)

; good
(zero? num)

---

style/filter-complement

Enabled by default	Version Added	Version Updated
true	0.1	1.2.0

Check for (filter (complement pred) coll).

Examples

; bad
(filter (complement even?) coll)

; good
(remove even? coll)

---

style/filter-vec-filterv

Enabled by default	Version Added	Version Updated
true	0.1	1.2.0

filterv is preferable for using transients.

Examples

; bad
(vec (filter pred coll))

; good
(filterv pred coll)

---

style/first-first

Enabled by default	Version Added	Version Updated
true	0.1	1.2.0

ffirst is succinct and meaningful.

Examples

; bad
(first (first coll))

; good
(ffirst coll)

---

style/first-next

Enabled by default	Version Added	Version Updated
true	0.1	1.2.0

fnext is succinct and meaningful.

Examples

; bad
(first (next coll))

; good
(fnext coll)

---

style/let-do

Enabled by default	Version Added	Version Updated
true	0.1	1.2.0

let has an implicit do, so use it.

Examples

; bad
(let [a 1 b 2] (do (println a) (println b)))

; good
(let [a 1 b 2] (println a) (println b))

---

style/mapcat-apply-apply

Enabled by default	Version Added	Version Updated
true	0.1	1.2.0

Check for (apply concat (apply map x y)).

Examples

; bad
(apply concat (apply map x y))

; good
(mapcat x y)

---

style/mapcat-concat-map

Enabled by default	Version Added	Version Updated
true	0.1	1.2.0

Check for (apply concat (map x y z)).

Examples

; bad
(apply concat (map x y))
(apply concat (map x y z))

; good
(mapcat x y)
(mapcat x y z)

---

style/minus-one

Enabled by default	Version Added	Version Updated
true	0.1	1.2.0

Checks for simple -1 that should use clojure.core/dec.

Examples

; bad
(- x 1)

; good
(dec x)

---

style/minus-zero

Enabled by default	Version Added	Version Updated
true	0.1	1.2.0

Checks for x - 0.

Examples

; bad
(- x 0)

; good
x

---

style/multiple-arity-order

Enabled by default	Version Added	Version Updated
true	1.3.0	1.3.0

Sort the arities of a function from fewest to most arguments.

Examples

; bad
(defn foo
  ([x] (foo x 1))
  ([x y & more] (reduce foo (+ x y) more))
  ([x y] (+ x y)))

; good
(defn foo
  ([x] (foo x 1))
  ([x y] (+ x y))
  ([x y & more] (reduce foo (+ x y) more)))

Reference

• https://guide.clojure.style/#multiple-arity-order

---

style/multiply-by-one

Enabled by default	Version Added	Version Updated
true	0.1	1.2.0

Checks for (* x 1).

Examples

; bad
(* x 1)
(* 1 x)

; good
x

---

style/multiply-by-zero

Enabled by default	Version Added	Version Updated
true	0.1	1.2.0

Checks for (* x 0).

Examples

; bad
(* x 0)
(* 0 x)

; good
0

---

style/neg-checks

Enabled by default	Version Added	Version Updated
true	0.1	1.2.0

neg? exists so use it.

Examples

; bad
(< num 0)
(> 0 num)

; good
(neg? num)

---

style/nested-addition

Enabled by default	Version Added	Version Updated
true	0.1	1.2.0

Checks for simple nested additions.

Examples

; bad
(+ x (+ y z))
(+ x (+ y z a))

; good
(+ x y z)
(+ x y z a)

---

style/nested-multiply

Enabled by default	Version Added	Version Updated
true	0.1	1.2.0

Checks for simple nested multiply.

Examples

; bad
(* x (* y z))
(* x (* y z a))

; good
(* x y z)
(* x y z a)

---

style/new-object

Enabled by default	Version Added	Version Updated
true	0.1.69	0.1.69

new is discouraged for dot usage.

Examples

; bad
(new java.util.ArrayList 100)

; good
(java.util.ArrayList. 100)

---

style/next-first

Enabled by default	Version Added	Version Updated
true	0.1	1.2.0

nfirst is succinct and meaningful.

Examples

; bad
(next (first coll))

; good
(nfirst coll)

---

style/next-next

Enabled by default	Version Added	Version Updated
true	0.1	1.2.0

nnext is succinct and meaningful.

Examples

; bad
(next (next coll))

; good
(nnext coll)

---

style/not-eq

Enabled by default	Version Added	Version Updated
true	0.1	1.2.0

not= exists, so use it.

Examples

; bad
(not (= num1 num2))

; good
(not= num1 num2)

Reference

• https://guide.clojure.style/#not-equal

---

style/not-nil?

Enabled by default	Version Added	Version Updated
true	0.1	1.2.0

some? exists so use it.

Examples

; bad
(not (nil? x))

; good
(some? x)

---

style/not-some-pred

Enabled by default	Version Added	Version Updated
true	0.1	1.2.0

not-any? is succinct and meaningful.

Examples

; bad
(not (some even? coll))

; good
(not-any? even? coll)

---

style/plus-one

Enabled by default	Version Added	Version Updated
true	0.1	1.2.0

Checks for simple +1 that should use clojure.core/inc.

Examples

; bad
(+ x 1)
(+ 1 x)

; good
(inc x)

---

style/plus-zero

Enabled by default	Version Added	Version Updated
true	0.1	1.2.0

Checks for x + 0.

Examples

; bad
(+ x 0)
(+ 0 x)

; good
x

---

style/pos-checks

Enabled by default	Version Added	Version Updated
true	0.1	1.2.0

pos? exists so use it.

Examples

; bad
(< 0 num)
(> num 0)

; good
(pos? num)

---

style/prefer-boolean

Enabled by default	Version Added	Version Updated
true	0.1.69	0.1.69

Use boolean if you must return true or false from an expression.

Examples

; bad
(if some-val true false)
(if (some-func) true false)

; good
(boolean some-val)
(boolean (some-func))

Reference

• https://guide.clojure.style/#converting-something-to-boolean

---

style/prefer-clj-math

Enabled by default	Version Added	Version Updated
true	0.1.69	0.1.69

NOTE: Requires Clojure version 1.11.0.

Prefer clojure.math to interop.

Examples

; bad
Math/PI
(Math/atan 45)

; good
clojure.math/PI
(clojure.math/atan 45)

Reference

• https://guide.clojure.style/#prefer-clojure-math-over-interop

---

style/prefer-clj-string

Enabled by default	Version Added	Version Updated
true	1.9.0	1.9.0

Prefer clojure.string to interop.

method	clojure.string
.contains	clojure.string/includes?
.endsWith	clojure.string/ends-with?
.replace	clojure.string/replace
.split	clojure.string/split
.startsWith	clojure.string/starts-with?
.toLowerCase	clojure.string/lower-case
.toUpperCase	clojure.string/upper-case
.trim	clojure.string/trim

Examples

; bad
(.toUpperCase "hello world")

; good
(clojure.string/upper-case "hello world")

Reference

• https://guide.clojure.style/#prefer-clojure-string-over-interop

---

style/prefer-condp

Enabled by default	Version Added	Version Updated
true	0.1.69	1.0

cond checking against the same value in every branch is a code smell.

This rule uses the first test-expr as the template to compare against each other test-expr. It has a number of conditions it checks as it runs:

• The cond is well-formed (aka even number of args).
• The cond has more than 1 pair.
• The first test-expr is a list with 3 forms.
• The function of every test-expr must match the test-expr of the first test-expr.
• The last test-expr isn't checked if it is true or a keyword.
• The last argument of every test-expr must match the last argument of the first test-expr.

Provided all of that is true, then the middle arguments of the test-exprs are gathered and rendered into a condp.

Examples

; bad
(cond
  (= 1 x) :one
  (= 2 x) :two
  (= 3 x) :three
  (= 4 x) :four)

; good
(condp = x
  1 :one
  2 :two
  3 :three
  4 :four)

; bad
(cond
  (= 1 x) :one
  (= 2 x) :two
  (= 3 x) :three
  :else :big)

; good
(condp = x
  1 :one
  2 :two
  3 :three
  :big)

Reference

• https://guide.clojure.style/#condp

---

style/prefer-vary-meta

Enabled by default	Version Added	Version Updated
true	0.1	0.1.69

vary-meta works like swap!, so no need to access and overwrite in two steps.

Examples

; bad
(with-meta x (assoc (meta x) :filename filename))

; good
(vary-meta x assoc :filename filename)

---

style/reduce-str

Enabled by default	Version Added	Version Updated
true	1.11	1.11

reduce calls the provided function on every element in the provided collection. Because of how str is implemented, a new string is created every time it's called. Better to rely on clojure.string/join's efficient StringBuilder and collection traversal.

Additionally, the 2-arity form of reduce returns the first item without calling str on it if it only has one item total, which is generally not what is expected when calling str on something.

Examples

; bad
(reduce str x)
(reduce str "" x)

; good
(clojure.string/join x)

---

style/redundant-let

Enabled by default	Version Added	Version Updated
true	0.1.69	0.1.69

Directly nested lets can be merged into a single let block.

Examples

; bad
(let [a 1]
  (let [b 2]
    (println a b)))

(let [a 1
      b 2]
  (println a b))

---

style/redundant-regex-constructor

Enabled by default	Version Added	Version Updated
true	1.10.0	1.10.0

Clojure regex literals (#"") are passed to java.util.regex.Pattern/compile at read time. re-pattern checks if the given arg is a Pattern, making it a no-op when given a regex literal.

Examples

; bad
(re-pattern #".*")

; good
#".*"

---

style/set-literal-as-fn

Enabled by default	Version Added	Version Updated
false	0.1.119	1.11

Sets can be used as functions and they're converted to static items when they contain constants, making them fairly fast. However, they're not as fast as [[case]] and their meaning is less clear at first glance.

Examples

; bad
(#{'a 'b 'c} elem)

; good
(case elem (a b c) elem nil)

---

style/single-key-in

Enabled by default	Version Added	Version Updated
true	0.1.69	0.1.69

assoc-in loops over the args, calling assoc for each key. If given a single key, just call assoc directly instead for performance and readability improvements.

Examples

; bad
(assoc-in coll [:k] 10)

; good
(assoc coll :k 10)

---

style/tostring

Enabled by default	Version Added	Version Updated
true	0.1	1.2.0

Convert (.toString) to (str).

Examples

; bad
(.toString x)

; good
(str x)

---

style/trivial-for

Enabled by default	Version Added	Version Updated
true	1.11	1.11

for is a complex and weighty macro. When simply applying a function to each element, better to rely on other built-ins.

Examples

; bad
(for [item items]
  (f item))

; good
(map f items)

Reference

• https://bsless.github.io/code-smells

---

style/update-in-assoc

Enabled by default	Version Added	Version Updated
true	0.1	1.2.0

update-in-ing an assoc with the same key are hard to read. assoc-in is known and idiomatic.

Examples

; bad
(update-in coll [:a :b] assoc 5)

; good
(assoc-in coll [:a :b] 5)

---

style/useless-do

Enabled by default	Version Added	Version Updated
true	0.1.69	1.2.0

A single item in a do is a no-op. However, it is sometimes necessary to wrap expressions in dos to avoid issues, so do surrounding ~@something will be skipped as well as #(do something).

Examples

; bad
(do coll)

; good
coll

; skipped
(do ~@body)
#(do [%1 %2])

---

style/when-do

Enabled by default	Version Added	Version Updated
true	0.1.69	1.2.0

when already defines an implicit do. Rely on it.

Examples

; bad
(when x (do (println :a) (println :b) :c))

; good
(when x (println :a) (println :b) :c)

---

style/when-not-call

Enabled by default	Version Added	Version Updated
true	0.1	1.2.0

when-not exists so use it lol.

Examples

; bad
(when (not x) :a :b :c)

; good
(when-not x :a :b :c)

---

style/when-not-do

Enabled by default	Version Added	Version Updated
true	0.1	1.2.0

when-not already defines an implicit do. Rely on it.

Examples

; bad
(when-not x (do (println :a) (println :b) :c))

; good
(when-not x (println :a) (println :b) :c)

---

style/when-not-empty?

Enabled by default	Version Added	Version Updated
true	0.1	0.1.69

seq returns nil when given an empty collection. empty? is implemented as (not (seq coll)) so it's best and fastest to use seq directly.

Examples

; bad
(when-not (empty? ?x) &&. ?y)

; good
(when (seq ?x) &&. ?y)

---

style/when-not-not

Enabled by default	Version Added	Version Updated
true	0.1	1.2.0

Two nots cancel each other out.

Examples

; bad
(when-not (not x) y z)

; good
(when x y z)