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2259 :: Redefine type properties

• hxsn (orginal) [2016-05-14T03:35:22+02:00] view original

  I'm trying to write a wrapper for a JSON format in which there is an array of Feature objects, all the same except for the format of the "coordinates" property. In order to combine these into one seq in Nim (to closely mirror the format), I set up the types as:

  type

  Feature* = ref object of RootObj

  featureType* : string properties* : seq[tuple[key: string, val: string]]

  Point* = ref object of Feature

  coordinates* : seq[float]

  MultiPoint* = ref object of Feature

  coordinates* : seq[seq[float]]

  and so on. The only difference between each is how the "coordinates" are defined.

  Nim will allow me to combine these into one seq (defined as seq[Feature]) without problems, and I can set the "featureType" and "properties" fields without issue. However, I can't set the "coordinates".

  If I leave the code as-is, I get the error "undeclared field: 'coordinates'", However, if I try to defined it in Feature first, I get the error "redefinition of 'coordinates'".

  Is there any way to allow redefinitions? I'm not much experienced with OOP in Nim, so apologies if this is a stupid question.

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• LeuGim (orginal) [2016-05-14T08:10:23+02:00] view original

  If Feature type by itself is not used (is abstract), you can just make it generic.

  type
    Feature*[T] = ref object of RootObj
      featureType* : string
      properties* : seq[tuple[key: string, val: string]]
      coordinates*: T
    Point* = Feature[seq[float]]
    MultiPoint* = Feature[seq[seq[float]]]
  
  # testing
  
  import typetraits
  proc test(f: Feature) =
    echo f.type.name, ": ", f.featureType, " at ", f.coordinates
  
  test(Point(
            featureType: "xxx",
            properties: @[("x","y")],
            coordinates: @[1.0,2.0,3.0]))
  var m = MultiPoint(
            featureType: "yyy",
            properties: @[("a","b"), ("c","d")],
            coordinates: @[@[1.0,2.0,3.0], @[4.0,5.0,6.0]])
  test(m)
  Run

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• hxsn (orginal) [2016-05-15T01:54:40+02:00] view original

  That works, thanks!

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