我尝试在Kubuntu 20操作系统上使用gcc-12将我的代码从C11标准升级到C20。我有一个自定义分配器：

namespace allocators {
template <class T,int n = 16384>
class ListAllocator : public std::allocator<T> {
public:
    typedef typename std::allocator<T>::size_type size_type;
    typedef typename std::allocator<T>::pointer pointer;
public:
    ListAllocator() : allocator<T>()                             {}
    ListAllocator(const ListAllocator<T,n>& a) : std::allocator<T>(a) {}
    ListAllocator(const allocator<T>& a) : std::allocator<T>(a)       {}

    char* _Charalloc(size_type N) {
        if (idx==0)
           return allocator<T>::_Charalloc(N);
        else
            return reinterpret_cast<char*>(arena[--idx]);
    }

    void deallocate(void* p, size_type s) {
        if (idx == n)
            allocator<T>::deallocate(p,s);
        else
            arena[idx++] = p;
    }

    static void deallocate() {
        while(idx) 
            ((allocator<T>*)0)->deallocate( reinterpret_cast<typename std::allocator<T>::pointer>(arena[--idx]) , size_type(sizeof(T)) );
    }

    static void*    arena[n];
    static size_t   idx;          // index of 1st emty field in arena
};

template <class T,int n>  void*  ListAllocator<T,n>::arena[n];
template <class T,int n>  size_t ListAllocator<T,n>::idx;

}

我有一个结构体，包含以下内容：

typedef T                           Coord;

  typedef std::pair<Coord , Coord >   Point;
  typedef ListAllocator<Point> ListPointAllocator;

  typedef std::list<Point2d,ListPointAllocator >   Pl;
  Pl*  plPtr;
  Point & edgeRef() { return beg ? plPtr->front() : plPtr->back();}

我得到错误：class std::__cxx11::list<std::pair<int, int>, std::ListAllocator<std::pair<int, int>, 16384> >'} has no member named 'front' class std::__cxx11::list<std::pair<int, int>, std::ListAllocator<std::pair<int, int>, 16384> >'} has no member named 'back'
我想找个解释，但什么也没找到。到底是什么问题呢？