On Mon, Jan 19, 2009 at 11:03 AM, Michael Reid <[email protected]> wrote:
>
> (defn index-of [#^String s #^String substr]
> (.indexOf s substr))
>
> Then the compiler will generate an optimized code path that directly
> invokes String.indexOf(String,String), and the other which will fall
> back to the reflective invocation. The reason that two code paths are
> needed is because Clojure is dynamically typed.
When sufficient hints are provided for the compiler to find exactly
one matching function, only one path is produced.
(defn get-first-char [#^String s]
(let [buf (make-array Character/TYPE 1)]
(.getChars s 0 1 buf 0) (first buf)))
Calling this with a String works fine:
user=> (get-first-char "foo")
\f
But using a StringBuffer, causes an exception:
user=> (get-first-char (StringBuffer. "foo"))
java.lang.ClassCastException: java.lang.StringBuffer cannot be cast to
java.lang.String (NO_SOURCE_FILE:0)
If you remove the #^String type hint, you'll see that both String and
StringBuffer work fine.
--Chouser
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