错误：静态断言失败：模板参数必须是完整的类或无界数组

问：

我从一个基类派生，我试图在其中定义一个类型。该类型通过变体依赖于自身，因此它需要在定义时知道基类的内存布局。但是，我不是过早地定义类型吗？所以我认为这会起作用，但它没有（CompilerExplorer）：

#include <variant>
#include <cstddef>
#include <array>


template <size_t V> struct container_base;
template <size_t V> struct container;

template <size_t V>
using val = std::variant<std::monostate, int, container_base<V>>;

template <size_t V>
struct container_base
{
    using iterator = typename std::array<val<V>, V>::iterator;
};

template <size_t V>
struct container : public container_base<V>
{
};

int main()
{
    container<100> A;
}

这将产生：

In file included from /opt/compiler-explorer/gcc-trunk-20220726/include/c++/13.0.0/variant:37,
                 from <source>:1:
/opt/compiler-explorer/gcc-trunk-20220726/include/c++/13.0.0/type_traits: In instantiation of 'struct std::is_copy_constructible<container_base<100> >':
/opt/compiler-explorer/gcc-trunk-20220726/include/c++/13.0.0/type_traits:3202:33:   required from 'constexpr const bool std::is_copy_constructible_v<container_base<100> >'
/opt/compiler-explorer/gcc-trunk-20220726/include/c++/13.0.0/variant:329:5:   required from 'constexpr const bool std::__detail::__variant::_Traits<std::monostate, int, container_base<100> >::_S_copy_ctor'
/opt/compiler-explorer/gcc-trunk-20220726/include/c++/13.0.0/variant:1334:11:   required from 'class std::variant<std::monostate, int, container_base<100> >'
/opt/compiler-explorer/gcc-trunk-20220726/include/c++/13.0.0/array:109:55:   required from 'struct std::array<std::variant<std::monostate, int, container_base<100> >, 100>'
<source>:15:11:   required from 'struct container_base<100>'
<source>:19:8:   required from 'struct container<100>'
<source>:25:20:   required from here
/opt/compiler-explorer/gcc-trunk-20220726/include/c++/13.0.0/type_traits:1012:52: error: static assertion failed: template argument must be a complete class or an unbounded array
 1012 |       static_assert(std::__is_complete_or_unbounded(__type_identity<_Tp>{}),
      |

我理解它，因此变体在首次使用时需要一个完整的类型才能使用（这是主要的！但是在那之前类型是完整的，所以我不知道为什么它不起作用。我能做些什么来解决这个问题？