std::collate<CharT>:: ~collate

From cppreference.com
Defined in header <locale>
protected : ~collate ( ) ;

Destructs a std:: collate facet. This destructor is protected and virtual (due to base class destructor being virtual). An object of type std:: collate , 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:: collate and implements a public destructor.

Example

#include <iostream>
#include <locale>
 
struct Destructible_collate : public std::collate<wchar_t>
{
    Destructible_collate(std::size_t refs = 0) : collate(refs) {}
    // note: the implicit destructor is public
};
 
int main()
{
    Destructible_collate dc;
    // std::collate<wchar_t> c; // compile error: protected destructor
}