protocol-ize with-open

Description

Good use (and documentation example) of protocols: make with-open aware of a Closable protocol for APIs that use a different close convention. See http://groups.google.com/group/clojure/browse_thread/thread/86c87e1fc4b1347c

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Andy Fingerhut
April 2, 2012, 6:11 PM

Patch 0001-Added-ClosableResource-protocol-for-with-open.patch dated 08/Mar/12 applies, builds, and tests cleanly on latest master as of Apr 2 2012. Tassilo has signed a CA.

Tassilo Horn
April 13, 2012, 5:23 PM

Updated patch to apply cleanly against master again.

Brandon Bloom
July 23, 2014, 3:00 AM

I looked up this ticket because I ran in to a reflection warning: with-open does not hint it's binding with java.io.Closeable

Some feedback on the patch:

1) This is a breaking change for anyone relying on the close method to be duck-typed.

2) CloseableResource is a bit long. clojure.core.protocols.Closeable is plenty unambiguous.

3) Rather than extending CloseableResource to java.io.Closeable, you can use the little known (undocumented? unsupported?) :on-interface directive:

That would perform much better than the existing patch.

Tassilo Horn
July 23, 2014, 1:12 PM

Hi Brandon, two questions:

Could 1) be circumvented somehow by providing a default implementation somehow? I guess the protocol could be extended upon Object with implementation (.close this), but that would give a reflection warning since Object has no close method. Probably one could extend upon Object and in the implementation search a "close" method using java.lang.reflect and throw an exception if none could be found?

Could you please tell me a bit more about the :on-interface option? How does that differ from extend? And how do I add the implementation, i.e., (.close this) with that option?

Enzzo Cavallo
May 19, 2020, 11:37 PM
  • Since clojure 1.10, Clojure only support java 8+, so AutoClosable can be used without any problem

  • There is some way to not break dynamic dispatch?

  • extend-with-metadata can be used?

https://github.com/clojure/clojure/blob/master/changes.md#11-java

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