Function is_inline

include/pybind11/detail/argument_vector.h:111–124

    }

    bool is_inline() const {
        // It is undefined behavior to access the inactive member of a
        // union directly. However, it is well-defined to reinterpret_cast any
        // pointer into a pointer to char and examine it as an array
        // of bytes. See
        // https://dev-discuss.pytorch.org/t/unionizing-for-profit-how-to-exploit-the-power-of-unions-in-c/444#the-memcpy-loophole-4
        bool result = false;
        static_assert(offsetof(inline_array, is_inline) == 0,
                      "untagged union implementation relies on this");
        static_assert(offsetof(heap_vector, is_inline) == 0,
                      "untagged union implementation relies on this");
        std::memcpy(&result, reinterpret_cast<const char *>(this), sizeof(bool));
        return result;
    }
};

template <typename T, std::size_t InlineSize>