Using template resulting type for auto

Question

In case I don’t want to call the std::ranges::subrange in the code below and want only to create a range object which will hold the results of the template function call later, what is the correct way to declare range?

I guess decltype should help here, but I can’t figure out the way to represent the type.

Reasoning

I will be able to provide first data for range only in the loop which will follow and I will need to use it after the loop ends, so I need this object outside the loop and not initialized at the beginning. Sometimes this is hard or even next to impossible.

The code

#include <ranges>
#include <vector>

int main()
{
    std::vector<int> values(10);

    // How to replace this with default initialization for range based on type only, 
    // without the call to std::ranges::subrange ?
    auto range = std::ranges::subrange(values.begin(), values.end());

    while (...) {
        range = std::ranges::equal_range(...);
    }

    size_t last_range_size = range.size();
}

Answer 1

The type you need is : std::ranges::subrange<std::vector<int>::iterator> as shown here

#include <ranges>
#include <vector>
#include <type_traits>

int main()
{
    std::vector<int> values(10);

    // How to replace this with default initialization for range based on type only, 
    // without the call to std::ranges::subrange ?
    auto range = std::ranges::subrange(values.begin(), values.end());

    // From https://en.cppreference.com/w/cpp/ranges/subrange
    // it follows this is the type : 
    using range_t = std::ranges::subrange<std::vector<int>::iterator>;

    // And this verifies the type equality
    static_assert(std::is_same_v<decltype(range),range_t>);
}