On 22 Mar 2010, at 14:12, Per Vognsen wrote:
Even if the functions can be written in terms of the core protocol,
putting them in the protocol makes it possible to implement
higher-performance specialized versions for some containers while
supplying default implementations in terms of the core protocol
functions via mixins. This is how Scala's Seq trait is designed:
Even though I don't like "me too" posts, I'll make an exception here
because I think this is a very important point. I have an example in
Clojure in my multiarray library:
http://code.google.com/p/clj-multiarray/source/browse/src/multiarray/protocol.clj
The function "rank" in MultiArrayProtocol is redundant in that it can
always be implemented as
(defn rank [x] (count (shape x)))
However, for some implementations, "rank" could just return an integer
field from a data structure, instead of constructing a vector for no
other purpose than count the number of elements in it. That's why
"rank" is a protocol function.
Konrad.
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