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1133 :: Converters only allowed at top level?

• winksaville (orginal) [2015-04-14T23:36:53+02:00] view original

  I created a type in a unittest and wanted to create a converter and got a compile error that converters are only allowed at the top level. Below is a simple example, what makes converters so special that they can only be defined at the top level? This is 0.10.3 as of today.

  $ nim -v ; cat -n x.nim ; nim c --hints:off x.nim
  Nim Compiler Version 0.10.3 (2015-04-14) [Linux: amd64]
  Copyright (c) 2006-2015 by Andreas Rumpf
  
  git hash: e281d4137025c5ed310c388b05be90578a5c2ff9
  active boot switches: -d:release
       1	proc x() =
       2	  type
       3	    MyType = object
       4	      id: int
       5
       6	  converter toInt(mt: MyType): int =
       7	    result = cast[int](mt.id)
       8
       9	  var
      10	    mt: MyType
      11	    i: int
      12
      13	  mt.id = 3
      14	  i = mt.toInt()
      15	  echo "mt=", mt, " i=", i
  x.nim(6, 2) Error: 'converter' is only allowed at top level
  Run

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• Araq (orginal) [2015-04-16T20:11:13+02:00] view original

  A converter is a cruel way to extend Nim's type system and so it's hard to tie it to a scope in the implementation. And if we cannot tie it to a scope, it has to be at the top level. Fortunately it doesn't matter since local converters make no sense anyway. In a proc scope it's easy enough to define a template `?`(x: untyped): untyped = cast[int](mt.id) and use that one additional character when you need it. ;-)

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• winksaville (orginal) [2015-04-17T01:55:01+02:00] view original

  It seems odd we can add local types, procs, templates... but not converters.

  Is this a limitation of the compiler implementation and could be addressed with effort or actually limitation of the language definition in some way?

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• Araq (orginal) [2015-04-17T10:43:19+02:00] view original

  Could be addressed with effort like most other things. But I don't see the point.

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