Mirror of forum.nim-lang.org

9050 :: `$` not working on custom type when imported in other modules

• solomonthewise (orginal) [2022-03-27T19:06:32+02:00] view original

  I defined a type called int_b = int64 and defined a specific print format for it using $. It works within the module its defined in however when I attempt to print a int_b in another module I get this error message. I made sure to add the * so it would import. I'm likely making a stupid mistake but I am not sure what. thanks

  here is the error message. this does not occur in the module its defined in though

  Error: type mismatch: got <Int_b>

  but expected one of:

  proc echo(x: varargs[typed, $])

  first type mismatch at position: 1 required type for x: varargs[typed] but expression 'b.player1' is of type: Int_b

  here is the code func $`*(i: Int_b): string = i.lis.mapIt(it.join("")).join("\n")`

---

• Yardanico (orginal) [2022-03-27T19:17:03+02:00] view original

  For anyone curious for the exact source code, this seems to reproduce the problem:

  # lib.nim
  type
    Int_b* = int64
  
  func `$`*(i: Int_b): string =
    "somestring"
  Run

  # main.nim
  import lib
  
  var a: Int_b
  echo a
  Run

  If you make Int_b a distinct int64 - it works, so I'm not 100% sure if this is a bug. I've tried searching existing issues, but nothing similar came up.

---

• z_____________ (orginal) [2022-03-27T19:23:54+02:00] view original

  If we call $ explicitly, we get a more illuminating error message:

  Error: ambiguous call; both dollars.$(x: int64) [proc declared in /path/to/lib/system/dollars.nim(14, 6)] and lib.$(i: Int_b) [func declared in /path/to/lib.nim(3, 6)] match for: (Int_b)

---

• Yardanico (orginal) [2022-03-27T19:25:14+02:00] view original

  Ah, right, it's not a big - if you want to have a custom $, you need to use distinct int64 instead. The reason is that int64 already has $ defined for it, so they conflict. It works in the same file because the local $ overrides the global one AFAIK.

---

• ynfle (orginal) [2022-03-27T19:54:02+02:00] view original

  I solution (depending what's in the file) could be to include it

---

• huantian (orginal) [2022-03-27T20:01:23+02:00] view original

  Using include like that is usually not the best idea unless you’ve thought about and understood your actions

---

• ynfle (orginal) [2022-03-27T20:07:27+02:00] view original

  Very true

---