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7363 :: How to write a template to call function with arbitrary number of arguments?

• alexeypetrushin (orginal) [2021-01-09T18:50:05+01:00] view original

  I'm working with lots of different time series data, and trying to make shortcuts for object initialisation, to write code like that:

  echo OptionParams.init_seq @[
    ("call", 120.0, 1.2), ("call", 120.0, 1.3), ("call", 120.0, 1.5),
    ("call", 160.0, 1.2), ("call", 160.0, 1.3), ("call", 160.0, 1.5)
  ]
  Run

  The problem is that T.init_seq function should accept tuples with arbitrary number of elements and translate it into the sequence of T.init calls.

  I'm currently using a separate init_seq function for every number of elements (for 1, 2, 3 number of elements) could it be written in a better, general way, to work with any N number of elements?

  playground

  import sequtils
  
  template init_seq*[R, A](_: type[R], list: seq[A]): seq[R] =
    list.map(proc (v: A): R = R.init(v))
  template init_seq*[R, A, B](_: type[R], list: seq[(A, B)]): seq[R] =
    list.map(proc (v: (A, B)): R = R.init(v[0], v[1]))
  template init_seq*[R, A, B, C](_: type[R], list: seq[(A, B, C)]): seq[R] =
    list.map(proc (v: (A, B, C)): R = R.init(v[0], v[1], v[2]))
  
  type OptionParams* = tuple
    right:     string
    tenor:     float
    moneyness: float
  
  func init*(_: type[OptionParams], right: string, tenor: float, moneyness: float): OptionParams =
    (right, tenor, moneyness)
  
  echo OptionParams.init_seq @[
    ("call", 120.0, 1.2), ("call", 120.0, 1.3), ("call", 120.0, 1.5),
    ("call", 160.0, 1.2), ("call", 160.0, 1.3), ("call", 160.0, 1.5)
  ]
  Run

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• xigoi (orginal) [2021-01-09T20:07:17+01:00] view original

  The templates tupleLen and get from typetraits should help.

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• xigoi (orginal) [2021-01-09T20:20:51+01:00] view original

  In this case, it looks like you'll need to make it a macro anyway, since you're also making lambdas with a variable number of arguments.

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• juancarlospaco (orginal) [2021-01-09T21:12:21+01:00] view original

  Template wont need strict concrete types https://play.nim-lang.org/#ix=2LsY

  The most close to Duck Typing-ish that you can get on Nim.

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• alexeypetrushin (orginal) [2021-01-09T21:39:33+01:00] view original

  Template wont need strict concrete types https://play.nim-lang.org/#ix=2LsY

  Hmm, I still don't know how to use it to expand the tuple.

  P.S.

  But with the addition of untyped to_seq it helped me to make code below possible :)

  template to_seq*(list: seq[untyped], R): seq[typeof R] = R.init_seq(list)
  
  echo @[
    ("call", 120.0, 1.2), ("call", 120.0, 1.3), ("call", 120.0, 1.5),
    ("call", 160.0, 1.2), ("call", 160.0, 1.3), ("call", 160.0, 1.5)
  ].to_seq(OptionParams)
  Run

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