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13495 :: What is the common type for all ref objects, just as ptr T can be safely converted to pointer

• hyu1996 (orginal) [2025-11-05T12:19:13+01:00] view original

  I've designed a context object that has a  `udata`  field. This field can store a reference to a user object, which is specified when the user creates the object. However, I'm not sure what type this field should be. I've tried  ref object  and  ref RootObj , but both result in compilation errors.

  
  import std/tables
  
  type
    CTX = object
      udata: ref RootObj
    A = ref object
    B = ref object
  
  var ctx = CTX()
  ctx.udata = A()
  ctx.udata = B()
  ctx.udata = newTable[int,int]()
  Run

  https://play.nim-lang.org/#pasty=FIxvAJtl

  A workaround is to use  pointer , and then handle  GC_ref  and GC_unref  in the hook.

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• Araq (orginal) [2025-11-05T13:44:15+01:00] view original

  RootRef is Nim's idiom for this. Yes ref int is not compatible to it, so people must put the int in a separate object. No big deal.

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• hyu1996 (orginal) [2025-11-05T14:23:24+01:00] view original

  After a quick test,  RootRef  is incompatible with generic ref object but compatible with ref object of RootObj. maybe I can force users to inherit from RootObj

  
  import std/tables
  
  type
    CTX = object
      udata: ref RootObj
    A = ref object
    B = ref object
    C = ref object of RootObj
  
  var ctx = CTX()
  #ctx.udata = A()
  #ctx.udata = B()
  #ctx.udata = newTable[int,int]()
  
  echo (A is RootRef)  # false
  echo (C is RootRef)  # true
  Run

  https://play.nim-lang.org/#pasty=hEMFfZrf

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• Araq (orginal) [2025-11-05T14:25:41+01:00] view original

  maybe I can force users to inherit from RootObj

  Yes. Your API, your rules.

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