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13429 :: shallowCopy in packedjson

• domogled (orginal) [2025-09-26T18:30:35+02:00] view original

  Hello community,

  I wanted to try using packedjson, but I ran into this error:

  Error: undeclared identifier: 'shallowCopy'

  https://forum.nim-lang.org/t/6549#40506

  shallowCopy and shallow might not do "shallow copies" anymore. Instead use system.move if you can or implement a copy-on-write datastructure.

  So I assume packedjson will not be updated to fix this — or will it?

  @Araq, am I understanding correctly that packedjson is more of a proof‑of‑concept, and that it’s generally recommended to use something like jsony or another maintained library instead?

  thanks

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• Araq (orginal) [2025-09-27T07:52:25+02:00] view original

  What are you talking about, packedjson supports arc/orc and compiles with Nim devel.

  Here is what it does:

  
          when defined(gcArc) or defined(gcOrc):
            x.t[][i] = move x.t[][i+diff]
          else:
            shallowCopy(x.t[][i], x.t[][i+diff])
  Run

  Which is appropriate. I think your problem here is a weird Nim configuration or installation.

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• arnetheduck (orginal) [2025-09-27T08:47:34+02:00] view original

  Which is appropriate

  in recent nim versions, is this still needed? ie wouldn't move have similar semantics?

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• planetis (orginal) [2025-09-27T11:21:41+02:00] view original

  I wish someone could explain what shallowCopy/move actually does in this case, when characters are copied one by one.

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• Araq (orginal) [2025-10-02T13:47:27+02:00] view original

  Sorry for the late reply but you're both right:

  1. The version without a when only using move should work for all memory management modes.
  2. Since it only copies single chars, a simple assignment would do, move has no advantage here.

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