constexpr_utils.hpp

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#pragma once
 
#include <cstddef>
#include <tuple>
#include <utility>
 
namespace bb {
namespace detail {
 
template <size_t Min, size_t Max, size_t Inc> constexpr auto make_index_range()
{
    static_assert(Max >= Min);
    static_assert(Inc >= 1);
    return []<size_t... Is>(std::index_sequence<Is...>) {
        return std::index_sequence<Min + (Is * Inc)...>{};
    }(std::make_index_sequence<(Max - Min - 1) / Inc + 1>{});
}
 
} // namespace detail
 
template <size_t Start, size_t End, size_t Inc, class F> constexpr void constexpr_for(F&& f)
{
    // F must be a template lambda with a single **typed** template parameter that represents the iterator
    // (e.g. [&]<size_t i>(){ ... } is good)
    // (and [&]<typename i>(){ ... } won't compile!)
    constexpr auto indices = detail::make_index_range<Start, End, Inc>();
    [&]<size_t... Is>(std::index_sequence<Is...>) { (f.template operator()<Is>(), ...); }(indices);
}
 
}; // namespace bb