# Using STL algorithms with Array

**URL:** <https://forum.juce.com/t/using-stl-algorithms-with-array/37073>\
**Category:** General JUCE discussion\
**Created:** [January 11, 2020, 12:08pm UTC](https://forum.juce.com/t/using-stl-algorithms-with-array/37073 "2020-01-11T12:08:36Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![LiamG](https://sea2.discourse-cdn.com/flex026/user_avatar/forum.juce.com/liamg/32/6844_2.png) [@LiamG](https://forum.juce.com/u/LiamG)\
**Post date:** [January 11, 2020, 12:08pm UTC](https://forum.juce.com/t/using-stl-algorithms-with-array/37073/1 "2020-01-11T12:08:36Z")

</div>

I regularly run into problems getting JUCE `Arrays` to work with STL set algorithms. I want to use STL as much as possible, but it’s not easy with JUCE.

For instance, this won’t compile:

```
    Array<int> newSet{ 1, 2, 3 },
               oldSet{ 2, 3, 4 },
               result;

        std::set_difference(newSet.begin(), newSet.end(),
                            oldSet.begin(), oldSet.end(),
                            std::back_inserter(result));

```

because the `back_inserter` can’t be created around an `Array`. So I often end up using `std::vector` instead of `Array`, but then I run into problems later when I have to convert one to the other element by element, which seems wasteful. I’m guessing I’m not the only person who struggles with this–it seems like it would be a common problem.

I have two questions:

1. Is there any way to get JUCE `Arrays` to work with stl algorithms, ie. some other option to `std::back_inserter`?

2. If not, what do people usually do? Abandon stl or find some fancy interface between `vectors` and `Arrays`?

---

<div class="post-metadata">

**Author:** ![reuk](https://sea2.discourse-cdn.com/flex026/user_avatar/forum.juce.com/reuk/32/21494_2.png) [@reuk](https://forum.juce.com/u/reuk)\
**Post date:** [January 11, 2020, 1:44pm UTC](https://forum.juce.com/t/using-stl-algorithms-with-array/37073/2 "2020-01-11T13:44:09Z")

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It’s fairly trivial to write your own output iterator, maybe something like this:

```cpp
template <typename Container> class BackAddIterator final {
public:
  BackAddIterator() noexcept = default;
  constexpr explicit BackAddIterator(Container &c)
      : container_(std::addressof(c)) {}

  template <typename T> constexpr BackAddIterator &operator=(T &&t) {
    container_->add(std::forward<T>(t));
    return *this;
  }

  constexpr BackAddIterator &operator*() { return *this; }
  constexpr BackAddIterator &operator++() { return *this; }
  constexpr BackAddIterator &operator++(int) { return *this; }

private:
  Container *container_{nullptr};
};

template <typename Container> constexpr auto backAdder(Container &c) {
  return BackAddIterator<Container>(c);
}

```

Then just call `backAdder` instead of `std::back_inserter`.

---

<div class="post-metadata">

**Author:** ![CrushedPixel](https://sea2.discourse-cdn.com/flex026/user_avatar/forum.juce.com/crushedpixel/32/8654_2.png) [@CrushedPixel](https://forum.juce.com/u/CrushedPixel)\
**Post date:** [January 11, 2020, 1:46pm UTC](https://forum.juce.com/t/using-stl-algorithms-with-array/37073/3 "2020-01-11T13:46:22Z")

</div>

Personally, I use `std::vector` whenever I need to do stuff that requires STL algorithms, or when I just want to iterate over the collection and not do anything fancy with it.

The only times I use `juce::Array` is when I want to use some of its convenience functions that don’t look as pretty when using STL algorithms, like `addIfNotAlreadyThere` or `removeAllInstancesOf`.

So basically, I default to using `std::vector`s, unless `juce::Array` makes the code prettier.

For context, in my current project I use `std::vector` 210 times, `juce::Array` 6 times and `juce::OwnedArray` 3 times.

---

<div class="post-metadata">

**Author:** ![LiamG](https://sea2.discourse-cdn.com/flex026/user_avatar/forum.juce.com/liamg/32/6844_2.png) [@LiamG](https://forum.juce.com/u/LiamG)\
**Post date:** [January 11, 2020, 1:56pm UTC](https://forum.juce.com/t/using-stl-algorithms-with-array/37073/4 "2020-01-11T13:56:37Z")

</div>

Thanks for the feedback. The thing is, I’m using a lot of other JUCE functions that give me `Arrays` not `vectors`, ie. `SelectedItemSet` and `var::getArray()`. Still, its good to know that other people approach it this way. For now, building my own iterator as @reuk suggested is definitely the right thing to do. I’m glad that other people here find this “trivial”, because it would have taken me hours!