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5959 :: private type in public API is allowed

• tim_st (orginal) [2020-02-20T21:00:18+01:00] view original

  When type T is defined private in file test.nim and a public proc p (returns T) is defined in this file too, and test is imported in test2.nim, test.p can be used there but test.T can't and at the same time test.p returns T. I saw that this is forbidden in rust (https://github.com/rust-lang/rust/issues/22261) and I think it makes sense to forbid it. IIRC Go allows it, like Nim.

  Was this discussed before for Nim?

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• Araq (orginal) [2020-02-20T23:08:59+01:00] view original

  I don't remember if it was discussed before but I don't see the problem. Never had a bug because of it, in the worst case you can use typeof until your dependency got fixed.

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• andrea (orginal) [2020-02-21T10:08:21+01:00] view original

  There's nothing wrong in this in my opinion. It just means that T is an opaque type. You can get it from exported functions, and pass it to other exported functions, but you can't create one yourself or manipulate one without using one of the functions in the module that exports it. I would even say that this is a useful pattern.

  For instance the following works:

  #dep.nim
  type T = object
    x: int
  
  proc makeT*(x: int): T = T(x: x)
  
  proc printT*(t: T) =
    echo t.x
  Run

  and then

  import dep
  
  let t = makeT(12)
  printT(t)
  Run

  but the following does not compile

  import dep
  
  let t = T(x:12)
  Run

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