On Wednesday, July 1, 2015 at 3:54:03 PM UTC-4, Jo Geraerts wrote:
>
> Hey,
>
> I when i tried to run my program with the shiny new 1.7, it broke. I have
> traced it down to the fact that zipmap (
> https://github.com/clojure/clojure/blame/master/src/clj/clojure/core.clj#L2940)
>
> does returns the keys in a different order than i'm used to.
>
> e.g clojure 1.6:
>
> nREPL server started on port 52315 on host 127.0.0.1 - nrepl://
> 127.0.0.1:52315
> REPL-y 0.3.5, nREPL 0.2.7
> Clojure 1.6.0
> Java HotSpot(TM) 64-Bit Server VM 1.8.0_40-b26
> Docs: (doc function-name-here)
> (find-doc "part-of-name-here")
> Source: (source function-name-here)
> Javadoc: (javadoc java-object-or-class-here)
> Exit: Control+D or (exit) or (quit)
> Results: Stored in vars *1, *2, *3, an exception in *e
>
> user=> (zipmap [:a :b] [:c :d])
> {:b :d, :a :c}
>
> Whereas clojure 1.7 does:
>
> nREPL server started on port 52193 on host 127.0.0.1 - nrepl://
> 127.0.0.1:52193
> REPL-y 0.3.5, nREPL 0.2.7
> Clojure 1.7.0
> Java HotSpot(TM) 64-Bit Server VM 1.8.0_40-b26
> Docs: (doc function-name-here)
> (find-doc "part-of-name-here")
> Source: (source function-name-here)
> Javadoc: (javadoc java-object-or-class-here)
> Exit: Control+D or (exit) or (quit)
> Results: Stored in vars *1, *2, *3, an exception in *e
>
> user=> (zipmap [:a :b] [:c :d])
> {:a :c, :b :d}
>
> As i'm using the keys function later on these values as a multimethod
> dispatch function, things break.
>
> It's rather trivial to change my program with the new ordering, but i was
> wondering if the ordering of the keys of the returned map is part of the
> contract.
>
> When one would need more context about the actual code, the usage of the
> zipmap can be found here at
> https://github.com/jgeraerts/imageresizer/blob/master/src/net/umask/imageresizer/urlparser.clj#L19
> .
> The multimethod dispatch
> https://github.com/jgeraerts/imageresizer/blob/master/src/net/umask/imageresizer/resizer.clj#L15
>
> The tests break with these kinds of exceptions:
>
> ERROR in (test-resizer) (MultiFn.java:156)
> expected: (= [200 [200 200]] (run-resizer "size/200x200/rose-cmyk.tiff"))
> 20:31:05.179 [main] WARN net.umask.imageresizer.resizer - image not found
> for uri size/200x200/nonexisting
> actual: java.lang.IllegalArgumentException: No method in multimethod
> 'scale' for dispatch value: (:width :height)
> at clojure.lang.MultiFn.getFn (MultiFn.java:156)
> clojure.lang.MultiFn.invoke (MultiFn.java:233)
>
> I'm glad to hear your feedback.
>
Key order for (non-sorted) maps is not guaranteed, but there is an easy
fix: pour the result of keys into a set, e.g. (into #{} (keys my-map)), and
use #{:width :height} e.g. as your dispatch values. Then it will work
independently of the vagaries of key ordering.
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