clojure.core/derive

View this page on ClojureDocs

Type: function Added: Clojure 1.0 Examples: 4 Runnable: 3

([tag parent] [h tag parent])

Establishes a parent/child relationship between parent and tag. Parent must be a namespace-qualified symbol or keyword and child can be either a namespace-qualified symbol or keyword or a class. h must be a hierarchy obtained from make-hierarchy, if not supplied defaults to, and modifies, the global hierarchy.

Examples

by gstamp on 2011-06-17 ▶

;; derive let you build a hierarchy but parents/ancestors/descendants and isa? let you query the hierarchy (derive ::rect ::shape) (derive ::square ::rect)

by OnesimusUnbound on 2011-08-10 ▶

(derive ::Cat ::Feline) nil (derive ::Lion ::Feline) nil (isa? ::Lion ::Feline) true (isa? ::Tuna ::Feline) false

by mhmdsalem1993 on 2017-08-19 . May have evaluation errors. ▶

(derive java.util.Map ::collection) (derive java.util.Collection ::collection) (isa? java.util.HashMap ::collection) -> true

by timgilbert on 2019-02-25 ▶

;; (derive) can be handy in multimethods that switch on field values: (def data [{:record/type :types/integer :record/number 123} {:record/type :types/float :record/number 123.45} {:record/type :types/text :record/text "hello"}]) (derive :types/float ::number) (derive :types/integer ::number) (derive :types/text ::text) (defmulti record-str :record/type) (defmethod record-str ::number [r] (str "Number: " (:record/number r))) (defmethod record-str ::text [r] (str "Text: " (:record/text r))) (map record-str data) ;; => ("Number: 123" "Number: 123.45" "Text: hello")

See also

• clojure.core/parents (1)
• clojure.core/ancestors (1)
• clojure.core/descendants (1)
• clojure.core/isa? (2)
• clojure.core/make-hierarchy (0)
• clojure.core/underive

---

Content from the matching ClojureDocs page, with authors credited on each contribution.