Type `IntoIter` is private

[ivan-aksamentov]

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The type IntoIter implemented in https://github.com/rust-ndarray/ndarray/pull/986 is not exposed publicly, which makes it difficult or impossible to implement IntoIterator trait for custom types wrapping ndarray:

use ndarray::iterators::IntoIter; // Module `iterators` is private

pub struct Foo {
  array: Array1<i32>,
}

impl IntoIterator for Foo {
  type Item = i32;
  type IntoIter = IntoIter<i32, Ix1>; // `IntoIter` is private
  fn into_iter(self) -> Self::IntoIter {
    self.array.into_iter()
  }
}

The type is private in it's own module, re-exported publicly from module iterators, however module iterators itself is not public in lib.rs: https://github.com/rust-ndarray/ndarray/blob/97ecc0db70d53a1119c7b03149fcd7207d4580bd/src/lib.rs#L191

The sibling types Iter and IterMut are exposed additionally in lib.rs https://github.com/rust-ndarray/ndarray/blob/97ecc0db70d53a1119c7b03149fcd7207d4580bd/src/lib.rs#L146

I believe that the reason why the author of the PR missed this is the unnecessary spaghetti of re-exports. There seem to be no particular pattern in place. Why is this complexity needed? How it can be improved?

Proposed changes:

• expose IntoIter publicly to solve this problem directly
• refactor public exports to avoid unnecessary complexity and prevent this kind of bugs from happening again
• add tests validating public interface of the library; require these tests to be added along with the new functionality in PRs affecting public interface

[bluss]

It should be in https://docs.rs/ndarray/latest/ndarray/iter/index.html and if it is not, it is a bug

[bluss]

I don't think it's impossible - <Array1<i32> as IntoIterator>::IntoIter should be available to you?