Avoiding reflection/hinting with byte-array.

[David Brown]

I can't figure out how to avoid reflection, in the 'update' method of
MessageDigest. It is overloaded on a single argument with either
'byte', 'byte[]', or 'java.nio.ByteBuffer'.

(import '(java.security MessageDigest))
(set! *warn-on-reflection* true)

The compiler didn't seem to like a tag that wasn't actually a class
name:

(def byte-array-class
(class (make-array Byte/TYPE 0)))

;; "Unable to resolve classname: byte-array-class"
(defn update1
[#^MessageDigest md #^{:tag byte-array-class} item]
(.update md item))

And it seems to have no effect if I expand it as the tag:

;; "call to update can't be resolved."
(defn update2
[#^MessageDigest md #^{:tag (class (make-array Byte/TYPE 0))} item]
(.update md item))

In this particular case, I was able to work around the issue one of
two ways, basically by using a different type.

(defn workaround
[#^MessageDigest md item]
(.update md item 0 (count item)))

(defn workaround2
[#^MessageDigest md item]
(.update md (java.nio.ByteBuffer/wrap item)))

Any ideas? BTW, my real use case is in a defmethod, where I handle
several other types for the update.

Thanks,
David

[Chouser]

On Sat, Nov 7, 2009 at 10:41 AM, David Brown <clo...@davidb.org> wrote:
>
> I can't figure out how to avoid reflection, in the 'update' method of
> MessageDigest.  It is overloaded on a single argument with either
> 'byte', 'byte[]', or 'java.nio.ByteBuffer'.
>
>   (import '(java.security MessageDigest))
>   (set! *warn-on-reflection* true)
>
> The compiler didn't seem to like a tag that wasn't actually a class
> name:
>
>   (def byte-array-class
>     (class (make-array Byte/TYPE 0)))
>
>   ;; "Unable to resolve classname: byte-array-class"
>   (defn update1
>     [#^MessageDigest md #^{:tag byte-array-class} item]
>     (.update md item))

Right, :tag values should be symbols, not classes or instances of
those classes. Most of those symbols name actual Java classnames
but a few other symbols are supported, mostly for arrays of
primitives:

objects Object[].class;
ints int[].class;
longs long[].class;
floats float[].class;
doubles double[].class;
chars char[].class;
shorts short[].class;
bytes byte[].class;
booleans boolean[].class;

This should work:

(defn update1 [#^MessageDigest md, #^bytes item]
(.update md item))

--Chouser

[David Brown]

On Sat, Nov 07, 2009 at 11:48:32AM -0500, Chouser wrote:

>This should work:
>
> (defn update1 [#^MessageDigest md, #^bytes item]
> (.update md item))

This does seem to work, thanks.

Any reason that 'doubles' is also defined as an array cast function,
but 'bytes' is not?

David

[Chouser]

I don't know of any deep reason.

Not only bytes, but also array-cast functions don't exist for
chars, shorts or booleans.

Also there are factory functions for several primitive array
types, but char-array, short-array, byte-array, and
boolean-array don't exist.

--Chouser

[Rich Hickey]

There is no deep reason. Patch welcome for unifying the array support
for primitives.

Rich