counted?

(counted? coll)

如果 coll 实现了常数复杂度的 count 操作,那么返回 true

; 向量、列表、Map 和集合的 count 操作都是常数复杂度的
; 但字符串不是

user=> (counted? [1 2 3])
true

user=> (counted? '(1 2 3))
true

user=> (counted? {:clojure "Rich"})
true

user=> (counted? #{:a :b :c})
true

user=> (counted? "string")
false

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