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7186 :: override decrement on indexed object

• jlindsay (orginal) [2020-12-01T17:02:08+01:00] view original

  One of the things that I love about Nim is the ease with which it allows for operator overloading. I can create a custom object like Array2D that allows me to index data by row and column values:

  func `[]=`*[T](self: var Array2d[T], row, column: int, value: T) {.inline.} =
    if row >= 0 and row < self.rows and column >= 0 and column < self.columns:
      self.values[row * self.columns + column] = value
  
  func `[]`*[T](self: Array2d[T], row, column: int): T  {.inline.} =
    if row < 0 or column < 0: return self.nodata
    if row >= self.rows or column >= self.columns: return self.nodata
    result = self.values[row * self.columns + column]
  Run

  And I can decrement by overloading the -= operator. However, I can't seem to figure out how I can combine these two. That is, I'd like to write:

  myArray[row, col] -= myValue
  Run

  Does anyone have suggestions? Thanks.

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• Araq (orginal) [2020-12-01T17:48:13+01:00] view original

  You need one more overload:

  func `[]`*[T](self: var Array2d[T], row, column: int): var T {.inline.} =
    if row < 0 or column < 0: return self.nodata
    if row >= self.rows or column >= self.columns: return self.nodata
    result = self.values[row * self.columns + column]
  Run

  (There is an RFC in the pipeline that redesigns this slightly...)

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• jlindsay (orginal) [2020-12-01T22:38:39+01:00] view original

  Interesting! I would never have imagined that that would do it. Thanks for pointing me to this Araq. If I may take this opportunity to tell you how much I appreciate all of your efforts with Nim. I have programmed in a lot of different languages but Nim is almost unique in the level of joy that it brings me when I use it. It has the perfect mix of ease to code and performance. I do a lot of Rust coding these days, which I think is also a great language. However, when I need to pump out a proof-of-concept, I reach for Nim, simply because it is so much easier to work with. I can't tell you enough how much I appreciate this language. I have even been pushing my graduate students to use it. Well done sir!

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