Improve support for extending protocols to primitive arrays
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Alex Miller April 29, 2024 at 2:44 PM
This is solved as a by-product of https://clojure.atlassian.net/browse/CLJ-2807#icft=CLJ-2807 which now provides an array class syntax.
```clojure
(extend-protocol P
byte/1 (p [_] "bytes")
int/1 (p [_] "ints"))
(p (byte-array 10)) ;; "bytes"
(p (int-array 10)) ;; "ints"
```
Greg Chapman March 18, 2017 at 5:04 PM
Using Class/forName has a further problem, as type-hints on the this parameter are longer emitted:
user=> (extend-protocol P (Class/forName "[B") (p [this] (aget this 0)))
Reflection warning, NO_SOURCE_PATH:2:50 - call to static method aget on clojure.lang.RT can't be resolved (argument types: unknown, int).Reflection warnings are also generated for non-primitive arrays (so just supporting ints etc, won't completely fix this problem). It would be good to have a solution which covered all the problems with extending protocols to arrays.
Alex Miller June 7, 2016 at 10:00 PM
On further inspection, I don't think this is a dupe of https://clojure.atlassian.net/browse/CLJ-1790#icft=CLJ-1790 but merely a related problem.
Alex Miller January 12, 2016 at 9:16 PM
nahuel September 19, 2014 at 12:08 AM
It also breaks when extending only one array type:
(extend-protocol P
String (p [_] "string")
(Class/forName "[B") (p [_] "ints")
)
;=> CompilerException java.lang.UnsupportedOperationException: nth not supported on this type ...But changing the declaration order fixes it:
(extend-protocol P
(Class/forName "[B") (p [_] "ints")
String (p [_] "string")
)
;=> OKDetails
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Alex MillerAlex MillerLabels
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It is possible to extend protocols to primitive arrays but specifying the class for the type is a little tricky:
(defprotocol P (p [_])) (extend-protocol P (Class/forName "[B") (p [_] "bytes")) (p (byte-array 0)) ;; => "bytes"However, things go bad if you try to do more than one of these:
(extend-protocol P (Class/forName "[B") (p [_] "bytes") (Class/forName "[I") (p [_] "ints")) CompilerException java.lang.UnsupportedOperationException: nth not supported on this type: Character, compiling:(NO_SOURCE_PATH:1:1) clojure.lang.Compiler.analyze (Compiler.java:6380) clojure.lang.Compiler.analyze (Compiler.java:6322) clojure.lang.Compiler$MapExpr.parse (Compiler.java:2879) clojure.lang.Compiler.analyze (Compiler.java:6369) clojure.lang.Compiler.analyze (Compiler.java:6322) clojure.lang.Compiler$InvokeExpr.parse (Compiler.java:3624) clojure.lang.Compiler.analyzeSeq (Compiler.java:6562) clojure.lang.Compiler.analyze (Compiler.java:6361) clojure.lang.Compiler.analyze (Compiler.java:6322) clojure.lang.Compiler$BodyExpr$Parser.parse (Compiler.java:5708) clojure.lang.Compiler$FnMethod.parse (Compiler.java:5139) clojure.lang.Compiler$FnExpr.parse (Compiler.java:3751) Caused by: UnsupportedOperationException nth not supported on this type: Character clojure.lang.RT.nthFrom (RT.java:857) clojure.lang.RT.nth (RT.java:807) clojure.core/emit-hinted-impl/hint--5951/fn--5953 (core_deftype.clj:758) clojure.core/map/fn--4207 (core.clj:2487) clojure.lang.LazySeq.sval (LazySeq.java:42) clojure.lang.LazySeq.seq (LazySeq.java:60) clojure.lang.RT.seq (RT.java:484) clojure.lang.RT.countFrom (RT.java:537) clojure.lang.RT.count (RT.java:530) clojure.lang.Cons.count (Cons.java:49) clojure.lang.Compiler.analyze (Compiler.java:6352) clojure.lang.Compiler.analyze (Compiler.java:6322)The code in {parse-impls} is seeing the second {(Class/forName "[I")} as a function, not as a new type. One workaround for this is to only extend the protocol to one type at a time.
It would be even better (moving into enhancement area) if there was a syntax here to specify primitive array types - we already have the syntax of {bytes, ints, longs}, etc for type hints and those seem perfectly good to me.