`clojure.core/ex-info`¶

Type: function Added: Clojure 1.4 Examples: 4 Runnable: 0

([msg map] [msg map cause])

Create an instance of ExceptionInfo, a RuntimeException subclass that carries a map of additional data.

Examples¶

by claj on 2015-02-15 . May have evaluation errors.

by humorless on 2019-06-24 . May have evaluation errors.

by daemianmack on 2020-01-28 . May have evaluation errors.

;; The 3-arg arity is for linking exceptions in accordance with Java convention.
;; For example you could write an exception wrapper:

(ns clojure.example)

(defn exception-wrapper
  "Wrap exceptions to embed `:event` information from the `request` such
  that we preserve the `Caused by` convention."
  [request exception]
  (let [event (:event request)
        exc (ex-info (.getMessage ^Throwable exception)
                     {:event event}
                     exception)]
    (throw exc)))

(exception-wrapper {:event "some-event-info"}
                                    (ex-info "Dang." {:trilobites :everywhere}))

;; => Execution error (ExceptionInfo) at clojure.example/eval5596 (REPL:26).
;; => Dang.

(clojure.repl/pst *e)
;; => ExceptionInfo Dang. {:event "some-event-info"}
;; =>    clojure.example/exception-wrapper (NO_SOURCE_FILE:7)
;; =>   [...]
;; =>    clojure.main/repl (main.clj:458)
;; => Caused by:
;; => ExceptionInfo Dang. {:trilobites :everywhere}

;; Like in Java, you should chain exceptions (ex-cause). 
;; This lets you rank the exception in context.
;; An exception chain is like an interrogation 
;; -> Who are you?              (type e) => clojure.lang.ExceptionInfo
;; -> What is your meaning?     (ex-message e) => Divide by Zero
;; -> Why did you behave badly? (ex-data e) => :divisor was 0
;; -> Who else was involved?    (ex-cause e) => #ArithmeticException{}
;; --> Who are you?             (-> e ex-cause type) => ArithmeticException
;; ---> Who are you?            (-> e ex-cause ex-cause type) => ...
(def a 1)
(def b 0)

(try (/ a b)
     (catch ArithmeticException ae          ;; <-- "defuse" Throwable
       (throw                               ;; <-- re-throw exception
         (ex-info                           ;; <-- contextualize ae
           (ex-message ae)                  ;; <-- chain exception message
           {:divisor b :dividend a}         ;; <-- give your new ex-info context
           ae))))                           ;; <-- chain ae as cause

by caumond on 2020-05-30 . May have evaluation errors.

clojure.core/ex-info¶

Examples¶

See also¶

`clojure.core/ex-info`¶