Due to an implementation detail in the library, a specialization of scoped_allocator_adaptor with two template arguments (example below) will cause a compilation error. #include <memory> #include <scoped_allocator> struct A00 : std::allocator<char> {   A00() {}   template <class P> A00(const P&) {} }; template <class T> struct A01 {   typedef T value_type;   A01() {}   template <class P> A01(const P&) {}   T* allocate(std::size_t n);   void deallocate(T* p, std::size_t n); }; template <class T> std::allocator<T> a02(void) {   return std::allocator<T>(); } int main() {    std::scoped_allocator_adaptor<A00> a00;    const std::scoped_allocator_adaptor<A00>& r00 = a00;    if (!noexcept(std::scoped_allocator_adaptor<A01<int>, A00>(                     a02<int>(), r00)))       return 1; }