Is there an equivalent to the range-based `enumerate` loop from python in modern C++?

Question

Is there an equivalent to the range-based enumerate loop from python in C++? I would imagine something like this.

enumerateLoop (auto counter, a         


        

Answer 1

C++17 and structured bindings makes this look OK - certainly better than some ugly mutable lambda with a local [i = 0](Element&) mutable or whatever I've done before admitting that probably not everything should be shoehorned into for_each() et al. - and than other solutions that require a counter with scope outside the for loop.

for (auto [it, end, i] = std::tuple{container.cbegin(), container.cend(), 0};
     it != end; ++it, ++i)
{
      // something that needs both `it` and `i`ndex
}

You could make this generic, if you use this pattern often enough:

template 
auto
its_and_idx(Container&& container)
{
    using std::begin, std::end;
    return std::tuple{begin(container), end(container), 0};
}

// ...

for (auto [it, end, i] = its_and_idx(foo); it != end; ++it, ++i)
{
    // something
}

---

C++ Standard proposal P2164 proposes to add views::enumerate, which would provide a view of a range giving both reference-to-element and index-of-element to a user iterating it.

We propose a view enumerate whose value type is a struct with 2 members index and value representing respectively the position and value of the elements in the adapted range.

[ . . .]

This feature exists in some form in Python, Rust, Go (backed into the language), and in many C++ libraries: ranges-v3, folly, boost::ranges (indexed).

The existence of this feature or lack thereof is the subject of recurring stackoverflow questions.

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