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3745 :: echo(1,2) != echo (1,2) ; where is this documented?

• timothee (orginal) [2018-04-12T02:37:21+02:00] view original

  echo(1,2) != echo (1,2) ; where is this documented?

  
  inim
  INim 0.2.0
  Nim Compiler Version 0.18.1 [MacOSX: amd64] at /Users/timothee/.nimble/bin/nim
  >>> echo (1,2)
  (Field0: 1, Field1: 2)
  >>> echo(1,2)
  12
  >>> echo (1,)
  1
  >>> echo (1)
  1
  Run

  • what are the rules on whether we're passing a single tuple argument or multiple arguments?
  • shouldn't echo (1,) be parsed as if we were passing a tuple of size 1, ie (Field0: 1) ?

  T* he only place I could find is this: https://nim-lang.org/docs/manual.html#syntax-precedence > Whether an operator is used a prefix operator is also affected by preceding whitespace (this parsing change was introduced with version 0.13.0):

  
  echo $foo
  # is parsed as
  echo($foo)
  Run

  however this doesn't describe the story above

  • https://github.com/nim-lang/Nim/wiki/Whitespace-FAQ also doesn't mention that
  • NOTE: not limited to echo, this is also case for the way this would work: macro foo*(n: varargs[untyped]): typed = ...
  • see also https://github.com/nim-lang/Nim/issues/7578 [RFC] let a=(1,) should return a tuple (int,) not an int

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• mashingan (orginal) [2018-04-12T07:02:22+02:00] view original

  What is the use of tuple with only one field?

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• Udiknedormin (orginal) [2018-04-12T10:19:05+02:00] view original

  @mashingan If any-length tuple is expected, a tuple with one or zeros elements is the right thing to use. It works really well with generic code on tuples.

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• timothee (orginal) [2018-04-12T10:44:56+02:00] view original

  • special casing 1-element tuples to not be tuples breaks generic code, eg:

  #nimble install tuples
  import tuples
  
  proc foo[T](a:T)=echo a.len
  
  foo(("abcdef", "ghi", "def")) # 3
  foo(("abcdef", "ghi")) #2
  foo(("abcdef", )) # 6 (oups!) instead of 1
  foo(()) # 0
  Run

  • same reason why fixed length arrays of size 1 exist, or named tuples of size 1 exist.

  EDIT

  • allows concatenating with singleton tuples with no ambiguity, eg:

  import tuples
  proc getCalculatorTestCases[Calculator]():auto =
    let a = (("1+1", 2), ("2*3", 6))
    when Calculator.supportsDivision:
      return a & (("8 / 2", 4),) # without 1 element tuple, this would be: (("1+1", 2), ("2*3", 6), "8 / 2", 4) which is not what we want here
    else:
      return a
  Run

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• mashingan (orginal) [2018-04-12T11:57:50+02:00] view original

  I agree when incomplete tuple creation should be an error instead.

  It's just, tuple for me just a convenient way to return multiple values. Usually I used it in helper procs that those just defined to help the main proc.

  So return tuple with only a field is kinda weird considering tuple is there to get multiple values.

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• timothee (orginal) [2018-04-16T02:42:40+02:00] view original

  hope the example i gave above was able to convince you. In any case (1,) is now supported.

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• Udiknedormin (orginal) [2018-04-16T14:27:13+02:00] view original

  @mashingan

  It is not. It's a common usecase, not the definition. You can use integers to denote count but that's not the definition of an integer.

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