non-nil-return for Java Fields

[cristian....@gmail.com]

Using non-nil-return has been really handy for Java methods that I know won't return null, but I'm having a similar issue when accessing (static) fields of classes. For example:

(ann len [String -> Integer])
(defn len [^String s]
    (.length s))

(len java.io.File/separator)

Will return an error:
Type Error (...) Type mismatch:

Expected:       java.lang.String

Actual:         (U String nil)
ExceptionInfo Type Checker: Found 1 error  clojure.core/ex-info (core.clj:4327)


Using non-nil-return doesn't seem to do anything (which makes sense since this isn't a method), but I can't seem to find an equivalent way to annotate that a field will not be nil. Is there a way to get around this?

Thanks,
Cristian

[Ambrose Bonnaire-Sergeant]

I don't think this is implemented. http://dev.clojure.org/jira/browse/CTYP-50

For now I recommend using something like when-let-fail to cast your value.

(len (when-let-fail [f java.io.File/separator] f))

[Di Xu]

Hi Cristian,

I'm not sure if typed clojure have this ability or not, but I've greped around, it seems it can't do this right now.

But you can get around this by:

(t/ann len [String -> Integer])

(defn len [^String s]

      (.length s))

(t/ann getFileSeparator [-> String])

(defn getFileSeparator []

  (let [s java.io.File/separator]

    (if s

      s

      (throw (RuntimeException. "impossible")))))

(len (getFileSeparator))

Thanks

Di Xu

[cristian....@gmail.com]

Thanks for the suggestions. For my purposes, I'm going with when-let-fail since I'm only experiencing the use of static fields at the public API level. For testing, when-let-fail is simpler and I don't anticipate users of the library using core.typed.

Thanks,
Cristian