std::num_get::~num_get

From cppreference.com
< cpp‎ | locale‎ | num get
Defined in header <locale>
protected: ~num_get();

Destructs a std::num_get facet. This destructor is protected and virtual (due to base class destructor being virtual). An object of type std::num_get, like most facets, can only be destroyed when the last std::locale object that implements this facet goes out of scope or if a user-defined class is derived from std::num_get and implements a public destructor.

[edit] Example

#include <iostream>
#include <locale>
struct Destructible_num_get : public std::num_get<wchar_t>
{
    Destructible_num_get(std::size_t refs = 0) : num_get(refs) {}
    ~Destructible_num_get() {}; // public dtor
};
int main()
{
    Destructible_num_get dc;
    // std::num_get<wchar_t> c;  // compile error: protected destructor
}