constexpr_indices.hpp

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#pragma once
 
/// @file userver/utils/constexpr_indices.hpp
/// @brief Functions for iterating over a constexpr range of integers
 
#include <cstddef>
#include <type_traits>
#include <utility>
 
USERVER_NAMESPACE_BEGIN
 
namespace utils {
 
namespace impl {
 
template <std::size_t... Indices, typename Func>
void DoForEachIndex(std::index_sequence<Indices...>, Func func) {
    static_assert(std::is_trivially_copyable_v<Func>);
    (..., func(std::integral_constant<std::size_t, Indices>{}));
}
 
template <std::size_t... Indices, typename Func>
void DoWithConstexprIndex(std::index_sequence<Indices...>, std::size_t runtime_index, Func func) {
    static_assert(std::is_trivially_copyable_v<Func>);
    (..., (runtime_index == Indices ? func(std::integral_constant<std::size_t, Indices>{}) : void()));
}
 
}  // namespace impl
 
/// Calls `func` with indices from range `0...<Count`, wrapped in
/// `std::integral_constant`.
template <std::size_t Count, typename Func>
void ForEachIndex(Func func) {
    impl::DoForEachIndex(std::make_index_sequence<Count>{}, func);
}
 
/// Calls `func` with `runtime_index` wrapped in `std::integral_constant`.
template <std::size_t Count, typename Func>
void WithConstexprIndex(std::size_t runtime_index, Func func) {
    impl::DoWithConstexprIndex(std::make_index_sequence<Count>{}, runtime_index, func);
}
 
}  // namespace utils
 
USERVER_NAMESPACE_END