iterator items*[T](a: openArray[T]): T {.inline.} =
  ## Iterates over each item of `a`.
  var i = 0
  while i < len(a):
    yield a[i]
    inc(i)

iterator mitems*[T](a: var openArray[T]): var T {.inline.} =
  ## Iterates over each item of `a` so that you can modify the yielded value.
  var i = 0
  while i < len(a):
    yield a[i]
    inc(i)

iterator items*[IX, T](a: array[IX, T]): T {.inline.} =
  ## Iterates over each item of `a`.
  var i = low(IX)
  if i <= high(IX):
    while true:
      yield a[i]
      if i >= high(IX): break
      inc(i)

iterator mitems*[IX, T](a: var array[IX, T]): var T {.inline.} =
  ## Iterates over each item of `a` so that you can modify the yielded value.
  var i = low(IX)
  if i <= high(IX):
    while true:
      yield a[i]
      if i >= high(IX): break
      inc(i)

iterator items*[T](a: set[T]): T {.inline.} =
  ## Iterates over each element of `a`. `items` iterates only over the
  ## elements that are really in the set (and not over the ones the set is
  ## able to hold).
  var i = low(T).int
  while i <= high(T).int:
    if T(i) in a: yield T(i)
    inc(i)

iterator items*(a: cstring): char {.inline.} =
  ## Iterates over each item of `a`.
  when defined(js):
    var i = 0
    var L = len(a)
    while i < L:
      yield a[i]
      inc(i)
  else:
    var i = 0
    while a[i] != '\0':
      yield a[i]
      inc(i)

iterator mitems*(a: var cstring): var char {.inline.} =
  ## Iterates over each item of `a` so that you can modify the yielded value.
  when defined(js):
    var i = 0
    var L = len(a)
    while i < L:
      yield a[i]
      inc(i)
  else:
    var i = 0
    while a[i] != '\0':
      yield a[i]
      inc(i)

iterator items*(E: typedesc[enum]): E =
  ## Iterates over the values of the enum ``E``.
  for v in low(E) .. high(E):
    yield v

iterator items*[T](s: HSlice[T, T]): T =
  ## Iterates over the slice `s`, yielding each value between `s.a` and `s.b`
  ## (inclusively).
  for x in s.a .. s.b:
    yield x

iterator pairs*[T](a: openArray[T]): tuple[key: int, val: T] {.inline.} =
  ## Iterates over each item of `a`. Yields ``(index, a[index])`` pairs.
  var i = 0
  while i < len(a):
    yield (i, a[i])
    inc(i)

iterator mpairs*[T](a: var openArray[T]): tuple[key:int, val:var T]{.inline.} =
  ## Iterates over each item of `a`. Yields ``(index, a[index])`` pairs.
  ## ``a[index]`` can be modified.
  var i = 0
  while i < len(a):
    yield (i, a[i])
    inc(i)

iterator pairs*[IX, T](a: array[IX, T]): tuple[key: IX, val: T] {.inline.} =
  ## Iterates over each item of `a`. Yields ``(index, a[index])`` pairs.
  var i = low(IX)
  if i <= high(IX):
    while true:
      yield (i, a[i])
      if i >= high(IX): break
      inc(i)

iterator mpairs*[IX, T](a:var array[IX, T]):tuple[key:IX,val:var T] {.inline.} =
  ## Iterates over each item of `a`. Yields ``(index, a[index])`` pairs.
  ## ``a[index]`` can be modified.
  var i = low(IX)
  if i <= high(IX):
    while true:
      yield (i, a[i])
      if i >= high(IX): break
      inc(i)

iterator pairs*[T](a: seq[T]): tuple[key: int, val: T] {.inline.} =
  ## Iterates over each item of `a`. Yields ``(index, a[index])`` pairs.
  var i = 0
  let L = len(a)
  while i < L:
    yield (i, a[i])
    inc(i)
    assert(len(a) == L, "the length of the seq changed while iterating over it")

iterator mpairs*[T](a: var seq[T]): tuple[key: int, val: var T] {.inline.} =
  ## Iterates over each item of `a`. Yields ``(index, a[index])`` pairs.
  ## ``a[index]`` can be modified.
  var i = 0
  let L = len(a)
  while i < L:
    yield (i, a[i])
    inc(i)
    assert(len(a) == L, "the length of the seq changed while iterating over it")

iterator pairs*(a: string): tuple[key: int, val: char] {.inline.} =
  ## Iterates over each item of `a`. Yields ``(index, a[index])`` pairs.
  var i = 0
  let L = len(a)
  while i < L:
    yield (i, a[i])
    inc(i)
    assert(len(a) == L, "the length of the string changed while iterating over it")

iterator mpairs*(a: var string): tuple[key: int, val: var char] {.inline.} =
  ## Iterates over each item of `a`. Yields ``(index, a[index])`` pairs.
  ## ``a[index]`` can be modified.
  var i = 0
  let L = len(a)
  while i < L:
    yield (i, a[i])
    inc(i)
    assert(len(a) == L, "the length of the string changed while iterating over it")

iterator pairs*(a: cstring): tuple[key: int, val: char] {.inline.} =
  ## Iterates over each item of `a`. Yields ``(index, a[index])`` pairs.
  when defined(js):
    var i = 0
    var L = len(a)
    while i < L:
      yield (i, a[i])
      inc(i)
  else:
    var i = 0
    while a[i] != '\0':
      yield (i, a[i])
      inc(i)

iterator mpairs*(a: var cstring): tuple[key: int, val: var char] {.inline.} =
  ## Iterates over each item of `a`. Yields ``(index, a[index])`` pairs.
  ## ``a[index]`` can be modified.
  when defined(js):
    var i = 0
    var L = len(a)
    while i < L:
      yield (i, a[i])
      inc(i)
  else:
    var i = 0
    while a[i] != '\0':
      yield (i, a[i])
      inc(i)


iterator items*[T](a: seq[T]): T {.inline.} =
  ## Iterates over each item of `a`.
  var i = 0
  let L = len(a)
  while i < L:
    yield a[i]
    inc(i)
    assert(len(a) == L, "the length of the seq changed while iterating over it")

iterator mitems*[T](a: var seq[T]): var T {.inline.} =
  ## Iterates over each item of `a` so that you can modify the yielded value.
  var i = 0
  let L = len(a)
  while i < L:
    yield a[i]
    inc(i)
    assert(len(a) == L, "the length of the seq changed while iterating over it")

iterator items*(a: string): char {.inline.} =
  ## Iterates over each item of `a`.
  var i = 0
  let L = len(a)
  while i < L:
    yield a[i]
    inc(i)
    assert(len(a) == L, "the length of the string changed while iterating over it")

iterator mitems*(a: var string): var char {.inline.} =
  ## Iterates over each item of `a` so that you can modify the yielded value.
  var i = 0
  let L = len(a)
  while i < L:
    yield a[i]
    inc(i)
    assert(len(a) == L, "the length of the string changed while iterating over it")


iterator fields*[T: tuple|object](x: T): RootObj {.
  magic: "Fields", noSideEffect.}
  ## Iterates over every field of `x`.
  ##
  ## **Warning**: This really transforms the 'for' and unrolls the loop.
  ## The current implementation also has a bug
  ## that affects symbol binding in the loop body.
iterator fields*[S:tuple|object, T:tuple|object](x: S, y: T): tuple[a,b: untyped] {.
  magic: "Fields", noSideEffect.}
  ## Iterates over every field of `x` and `y`.
  ##
  ## **Warning**: This really transforms the 'for' and unrolls the loop.
  ## The current implementation also has a bug that affects symbol binding
  ## in the loop body.
iterator fieldPairs*[T: tuple|object](x: T): RootObj {.
  magic: "FieldPairs", noSideEffect.}
  ## Iterates over every field of `x` returning their name and value.
  ##
  ## When you iterate over objects with different field types you have to use
  ## the compile time ``when`` instead of a runtime ``if`` to select the code
  ## you want to run for each type. To perform the comparison use the `is
  ## operator <manual.html#generics-is-operator>`_. Example:
  ##
  ## .. code-block:: Nim
  ##   type
  ##     Custom = object
  ##       foo: string
  ##       bar: bool
  ##
  ##   proc `$`(x: Custom): string =
  ##     result = "Custom:"
  ##     for name, value in x.fieldPairs:
  ##       when value is bool:
  ##         result.add("\n\t" & name & " is " & $value)
  ##       else:
  ##         if value.isNil:
  ##           result.add("\n\t" & name & " (nil)")
  ##         else:
  ##           result.add("\n\t" & name & " '" & value & "'")
  ##
  ## Another way to do the same without ``when`` is to leave the task of
  ## picking the appropriate code to a secondary proc which you overload for
  ## each field type and pass the `value` to.
  ##
  ## **Warning**: This really transforms the 'for' and unrolls the loop. The
  ## current implementation also has a bug that affects symbol binding in the
  ## loop body.

iterator fieldPairs*[S: tuple|object, T: tuple|object](x: S, y: T): tuple[
  a, b: untyped] {.
  magic: "FieldPairs", noSideEffect.}
  ## Iterates over every field of `x` and `y`.
  ##
  ## **Warning**: This really transforms the 'for' and unrolls the loop.
  ## The current implementation also has a bug that affects symbol binding
  ## in the loop body.
