Automatically managing memory with std::unique_ptr<T>

The fundamental properties of a smart pointer type are simple: it should support operator*, and it should overload the special member functions to preserve its class invariants, whatever those are.

std::unique_ptr<T> supports the same interface as T*, but with the class invariant that, once you construct a unique_ptr pointing to a given heap-allocated object, that object will be freed when the destructor unique_ptr is called. Let's write some code supporting that T* interface:

    template<typename T>
    class unique_ptr {
      T *m_ptr = nullptr;
    public:
      constexpr unique_ptr() noexcept = default;
      constexpr unique_ptr(T *p) noexcept : m_ptr(p) {}

      T *get() const noexcept { return m_ptr; }
      operator bool() const noexcept { return bool(get()); }
      T& operator*() const noexcept { return *get(); }
      T* operator->() const noexcept { return get(); }

If we stopped here--with just a way...