1  
       2  template<typename _Tp>
       3  class allocator {};
       4  
       5  template<typename _Alloc> struct allocator_traits;
       6  
       7  template<typename _Tp>
       8  struct allocator_traits <allocator<_Tp>>
       9  {
      10    using pointer = _Tp*;
      11  };
      12  
      13  struct mutex {};
      14  
      15  template<typename _Tp, typename _Alloc>
      16  class Inplace
      17  {
      18  public:
      19    virtual void _M_dispose() noexcept
      20    {
      21      // bogus error ambiguous partial specializations
      22      typename allocator_traits<_Alloc>::pointer v;
      23    }
      24  };
      25  
      26  inline void *
      27  allocate_shared()
      28  {
      29    return new Inplace<mutex, allocator<mutex>> ();
      30  }