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Practical examples of use for Clojure's some-> macro

Clojure 1.5 adds new threading macros, including:

  • some->
  • some->>

The changelog has this contrived example to illustrate how some-> works:

user=> (defn die [x] (assert false))
#'user/die
user=> (-> 1 inc range next next next die)
AssertionError Assert failed: false  user/die (NO_SOURCE_FILE:65)
user=> (some-> 1 inc range next next next die)
nil

Chatting with other programmers, we found it difficult to think of a good, practical example for some->. When have you used some-> to solve a real-world problem?

Solution

  • some-> can be used to "auto-guard" a threaded series of processing steps where some part in the chain (especially in the middle) might return nil which would cause a logic failure further down the chain.

    Particular examples could include threading clojure functions together with java interop where you would need to guard against null pointer exceptions.