How do I return a range view from a function?

Question

What is the right way to implement the function below to allow the caller to iterate over the range it returns?

#include <set>
#include <ranges>

std::set<int> set{1, 2, 3, 4, 5, 6, 7, 8, 9, 10};

auto find_range(int a)
{
    //What type should I return?
    return std::make_tuple(set.lower_bound(a - 3), set.upper_bound(a + 3));
}

int main()
{
    for (int x : find_range(5)) {...}
}

The function returns a couple of iterators pointing to 2 and 9, so the loop should iterate over 2, 3, 4, 5, 6, 7, 8.

I'm not sure what you're trying to return from the function. Could you show an example value of set and the desired output? — cigien
– cigien, Commented Sep 8, 2021 at 0:07
Are you looking to return a container or a view? Containers carry the data while views are based on some other source of data (which could be, e.g., a container or instructions for how to generate the sequence). — Qaz
– Qaz, Commented Sep 8, 2021 at 0:13

cigien · Accepted Answer · 2021-09-08 00:15:55Z

3

You can return a subrange like this

auto find_range(int a)
{
    return std::ranges::subrange(set.lower_bound(a - 3), 
                                 set.upper_bound(a + 3));
}

Here's a demo.

answered Sep 8, 2021 at 0:15

cigien

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