{.closure.} iterator can only be used once

[iacore]

Description

iterator abc: int {.closure.} =
  for i in [1, 2, 3]:
    yield i

proc defg(abc_inner: (iterator: int)) =
  echo "Iter 0"
  for i in abc_inner():
    echo i
  echo "Iter 1"
  for i in abc_inner():
    echo i

defg(abc)

Nim Version

Nim Compiler Version 1.6.10 [Linux: amd64]
Compiled at 2022-11-21
Copyright (c) 2006-2021 by Andreas Rumpf

git hash: f151925
active boot switches: -d:release

Current Output

Iter 0
1
2
3
Iter 1

Expected Output

Iter 0
1
2
3
Iter 1
1
2
3

Possible Solution

No response

Additional Information

No response

[bung87]

try below.

proc resetGen[T: proc](x: T, n: int) {.noSideEffect, inline.} =
    {.emit: """
    ((NI*) `x`.ClE_0)[1] = `n`;
    """.}
resetGen(yourIter,0)

[iacore]

try below.

proc resetGen[T: proc](x: T, n: int) {.noSideEffect, inline.} =
    {.emit: """
    ((NI*) `x`.ClE_0)[1] = `n`;
    """.}
resetGen(yourIter,0)

What is this?

[Araq]

This is not a bug. The abc in defg(abc) creates the closure iterator and you can only "drain" it once. You can recreate a closure iterator by another usage of abc. (Yes, this is subtle and should be documented.)

[iacore]

I thought closure is only created with abc(), and abc is pass-by-value (like all other nim concepts)
Same as abc() is a function call, but abc is the function itself.

[bung87]

it's called "reset generator", same like python, generator yield all value, so it will not do anything, reset its internal state so it become re-useable.