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5681 :: Why inherit RootObj?

• marks (orginal) [2019-12-13T22:16:09+01:00] view original

  According to the manual https://nim-lang.org/docs/system.html#RootObj

  "Objects should inherit from RootObj or one of its descendants."

  Why is this?

  The next sentence is:

  "However, objects that have no ancestor are also allowed."

  I've been doing this without problems.

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• treeform (orginal) [2019-12-14T01:00:00+01:00] view original

  Couldn't render post #35275.

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• c0ntribut0r (orginal) [2019-12-14T10:06:29+01:00] view original

  Disagreed. I use inheritance, methods and dynamic dispatch without RootObj.

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• AyJayKay (orginal) [2020-01-25T11:27:24+01:00] view original

  It probably should say "Object Oriented Programming style Classes should inherit from RootObj or one of its descendants."

  This wouldn't help really, since it is creating the same confusion. (At least for me.) I still don't understand why one should do it. What do I gain/loose putting it there or not?

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• reneha (orginal) [2020-01-26T20:24:26+01:00] view original

  Maybe the idea is that by inheriting RootObj you are stating that you are going to use OOP features, although inheriting from RootObj is not required for it.

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• Araq (orginal) [2020-01-26T20:35:03+01:00] view original

  It's comparable to how C++ does it: An object only needs the V-Table pointer if it can be inherited from. Now ... Nim doesn't use V-Tables so instead you inherit from RootObj to tell the compiler you need runtime type tags in the object. It's IMHO a slightly better design because interop between packages is easier when they all agree on a common base class.

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• reneha (orginal) [2020-01-26T20:45:34+01:00] view original

  Ah ok, so inheriting from RootObj does what 'is tagged' does in Ada. But this means that dynamic dispatch doesn't work without it, differently from what c0ntribut0r claimed.

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• solo989 (orginal) [2020-01-27T06:19:24+01:00] view original

  It's not technically required because you can do this this instead.

  type
    Hello {.inheritable.} = object
    Hello2 = object of Hello
  Run

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• Araq (orginal) [2020-01-27T08:18:51+01:00] view original

  Note that the quite common .inheritable, pure is unsafe and only for C/C++ interop. With pure there is no type tag so of cannot work and dynamic type conversions are unchecked. I know of no useful application of .inheritable without the .pure, better inherit from RootObj then.

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