DeadMG's `unique_ptr` wrapper for opaque types

unique_handle.cpp

#include <memory>

int open() { return 1; }
void close(int) {}

template<typename T, typename Deleter, Deleter d, T null_value = T{}>
struct value_deleter
{
    struct wrapper
    {
        T value;
        wrapper() : value{null_value} {}
        wrapper(T t) : value{t} {}
        wrapper(std::nullptr_t) : value{null_value} {}
        bool operator==(std::nullptr_t) { return value == null_value; }
        bool operator!=(std::nullptr_t) { return value != null_value; }
        T operator*() { return value; }
    };
    using pointer = wrapper;
    void operator()(wrapper w) {
        if (w.value != null_value)
            d(w.value);
    }
};

int main() {
    std::unique_ptr<int, value_deleter<int, decltype(&close), &close>> ptr(open());
}