std_variant_helpers.h

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#pragma once
 
#include <cstddef>
#include <type_traits>
#include <variant>
 
namespace osc
{
    namespace detail
    {
        // returns the index of the given variant type (impl)
        template<typename Variant, typename T, size_t I = 0>
        [[nodiscard]] constexpr size_t variant_index_impl()
        {
            if constexpr (I >= std::variant_size_v<Variant>) {
                return std::variant_size_v<Variant>;
            }
            else if constexpr (std::is_same_v<std::variant_alternative_t<I, Variant>, T>) {
                return I;
            }
            else {
                return variant_index_impl<Variant, T, I + 1>();
            }
        }
    }
 
    // returns the index of the given variant type
    template<typename Variant, typename T>
    [[nodiscard]] constexpr size_t variant_index()
    {
        return detail::variant_index_impl<Variant, T>();
    }
 
    template<typename... Ts>
    struct Overload : Ts... {
        using Ts::operator()...;
    };
    template<typename... Ts> Overload(Ts...) -> Overload<Ts...>;
}