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112 :: named Array properties

• adrianv (orginal) [2012-12-04T15:22:00+01:00] view original

  is there a trick to have named array properties ?

  I tried :

  
  
  type
    TFoo = object
      data: array[0..100, int]
  
  proc `[]` (self: var TFoo, x: int): var int =
    return self.data[x]
  
  proc `second[]` (self: var TFoo, x: int): var int =
    return self.data[2*x]
  
  var f: TFoo
  
  for i in 0..f.data.high: f[i] = 2 * i
  
  # echo f.second[1]
  
  echo `second[]`(f,1)
  # this is the only way I could use it, but not what I expected
  Run

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• Araq (orginal) [2012-12-04T18:47:13+01:00] view original

  You can do something like:

  
  
  type
    TFoo = object
      data: array[0..100, int]
    TSecond = distinct TFoo
  
  proc `[]` (self: var TFoo, x: int): var int =
    return self.data[x]
  
  proc `[]=` (self: var TFoo, x, y: int) =
    # only `[]` returning a 'var T' seems to not work for now :-/
    self.data[x] = y
  
  proc second(self: var TFoo): var TSecond =
    return TSecond(self)
  
  proc `[]`(self: var TSecond, x: int): var int =
    return TFoo(self).data[2*x]
  
  var f: TFoo
  
  for i in 0..f.data.high: f[i] = 2 * i
  
  echo f.second[1]
  Run

  But I would simply overload {} instead of second[].

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• adrianv (orginal) [2012-12-04T21:18:52+01:00] view original

  But I would simply overload {} instead of second[].

  agreed - for that simple task its to complicated, but anyway a nice trick with distinct. Many thanks.

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