std::unique_ptr<T,Deleter>::get_deleter

#include <iostream>
#include <memory>

struct Foo
{
    Foo() { std::cout << "Foo() 0x" << std::hex << (void*)this << '\n'; }
    ~Foo() { std::cout << "~Foo() 0x" << std::hex << (void*)this << '\n'; }
};
 
struct D
{
    int number;

    void bar()
    {
        std::cout << "call D::bar(), my number is: " << std::dec << number << '\n';
    }

    void operator()(Foo* p) const
    {
        std::cout << "call deleter for Foo object 0x" << std::hex << (void*)p << '\n';
        delete p;
    }
};

int main()
{
    std::cout << "main start\n";

    std::unique_ptr<Foo, D> up1(new Foo(), D(42));
    D& del1 = up1.get_deleter();
    del1.bar();

    std::unique_ptr<Foo, D> up2(new Foo(), D(43));
    D& del2 = up2.get_deleter();
    auto* released = up2.release();
    del2(released);

    std::cout << "main end\n";
}

Вывод:

main start
Foo() 0x0x90cc30
call D::bar(), my number is: 42
Foo() 0x0x90cc50
call deleter for Foo object 0x0x90cc50
~Foo() 0x0x90cc50
main end
call deleter for Foo object 0x0x90cc30
~Foo() 0x0x90cc30