not_null, C++ (gcc)

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#include <iostream>

template <class T>
class not_null
{
public:
    static_assert(std::is_assignable<T&, std::nullptr_t>::value, "T cannot be assigned nullptr.");

template <typename U, typename = std::enable_if_t<std::is_convertible<U, T>::value>>
    constexpr not_null(U&& u) : ptr_(std::forward<U>(u))
    {
        //Expects(ptr_ != nullptr);
    }

template <typename = std::enable_if_t<!std::is_same<std::nullptr_t, T>::value>>
    constexpr not_null(T u) : ptr_(u)
    {
        //Expects(ptr_ != nullptr);
    }

template <typename U, typename = std::enable_if_t<std::is_convertible<U, T>::value>>
    constexpr not_null(const not_null<U>& other) : not_null(other.get())
    {
    }

not_null(not_null&& other) = default;
    not_null(const not_null& other) = default;
    not_null& operator=(const not_null& other) = default;

constexpr T get() const
    {
        return ptr_;
    }

constexpr operator T() const { return get(); }
    constexpr T operator->() const { return get(); }
    constexpr decltype(auto) operator*() const { return *get(); }

// prevents compilation when someone attempts to assign a null pointer constant
    not_null(std::nullptr_t) = delete;
    not_null& operator=(std::nullptr_t) = delete;

private:
    T ptr_;
};

template <class T>
auto make_not_null(T&& t) {
    return not_null<std::remove_cv_t<std::remove_reference_t<T>>>{std::forward<T>(t)};
}

struct some{};

void foo(not_null<some> ){}

int main()
{
    some a;
    
    auto p = make_not_null(&a);
    
    
}

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Compilation time: 0.33 sec, absolute service time: 0,33 sec