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2972 :: Inline iterator chaining - Is manual correct?

• mratsim (orginal) [2017-05-25T14:46:02+02:00] view original

  According to the manual:

  An inline iterator is an iterator that's always inlined by the compiler leading to zero overhead for the abstraction, but may result in a heavy increase in code size. Inline iterators are second class citizens; They can be passed as parameters only to other inlining code facilities like templates, macros and other inline iterators.

  Several topics have already be raised on similar questions:

  • pairs with iterators in 2015
  • iterator as arg of iterator in 2016
  • zip for iterators in 2017

  In the end, all solutions resorted to using closure iterators instead. So is it possible to pass inline iterator to other inline iterator, if yes how? If no, I think manual should be updated.

  Test case with Python-like enumerate:

  let s = @[1, 2, 3, 4, 5]
  
  iterator values[T](s: seq[T]): T {.inline.}=
    # copy of `items` to test without its special meaning
    for val in s:
      yield val
  
  iterator enumerate[T](it: iterator {. inline .}): auto {.inline.}=
    var i = 0
    for val in it:
      yield (i, val)
      inc i
  
  iterator enumerate2[T](s: seq[T], it: iterator(a: seq[T]): T {. inline .}): T {.inline.}=
    var i = 0
    for val in s.it:
      yield (i, val)
      inc i
  
  
  # for tup in s.values.enumerate:
  #   echo tup
  # inline_it.nim(21, 20) Error: type mismatch: got (int)
  # but expected one of:
  # iterator enumerate[T](it: iterator): auto
  
  for tup in enumerate2(s, values):
    echo tup
  # inline_it.nim(27, 22) template/generic instantiation from here
  # inline_it.nim(16, 15) Error: type mismatch: got (int)
  # but expected one of:
  # iterator items[IX, T](a: array[IX, T]): T
  # iterator items(E: typedesc[enum]): E:type
  # iterator items(a: string): char
  # iterator items[T](s: Slice[T]): T
  # iterator items[T](a: openArray[T]): T
  # iterator items[T](a: set[T]): T
  # iterator items[T](a: seq[T]): T
  # iterator items(a: cstring): char
  Run

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• cdome (orginal) [2017-05-26T22:51:57+02:00] view original

  Hi,

  Unfortunately I am on vacation without access to my workstation with nim, so code will be schematic. This kind of approach works for me:

  type InlineIterator[T] = iterator: T {.inline.}
  
  let s = @[1, 2, 3, 4, 5]
  
  iterator values: type(s[0]) {.inline.} =
    # Make argumentless iterator
    for val in s:
      yield val
  
  
  iterator enumerate[T](it: InlineIterator[T]): (int,T) {.inline.} =
    var i = 0
    for val in it():
      yield (i, val)
      inc i
  
  for tup in enumerate(values):
    echo tup
  
  Run

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• cdome (orginal) [2017-05-26T23:04:20+02:00] view original

  Ok, I have tried my code at https://tio.run and it doesn't compile, because of a trivial to fix bug in compiler. You can try to fix it yourself, it is in proc semFor file semstmts.nim or you can wait until till end of next week when I will be back.

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• mratsim (orginal) [2017-05-27T07:49:24+02:00] view original

  Indeed, I get this error:

  playground_it.nim(17, 21) template/generic instantiation from here
  playground_it.nim(13, 16) Error: type mismatch: got (int)
  but expected one of:
  iterator items[IX, T](a: array[IX, T]): T
  iterator items(E: typedesc[enum]): E:type
  iterator items(a: string): char
  iterator items[T](s: Slice[T]): T
  iterator items[T](a: openArray[T]): T
  iterator items[T](a: set[T]): T
  iterator items[T](a: seq[T]): T
  iterator items(a: cstring): char
  Run

  I am not comfortable with modifying the compiler yet, I'll raise an issue on the bug tracker (or check if one is already existing)

  Edit: issue already reported: https://github.com/nim-lang/Nim/issues/4516

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