23 General utilities library [utilities]

23.11 Smart pointers [smartptr]

23.11.6 Class template enable_­shared_­from_­this [util.smartptr.enab]

A class T can inherit from enable_­shared_­from_­this<T> to inherit the shared_­from_­this member functions that obtain a shared_­ptr instance pointing to *this.
[Example
:
struct X: public enable_shared_from_this<X> { };

int main() {
  shared_ptr<X> p(new X);
  shared_ptr<X> q = p->shared_from_this();
  assert(p == q);
  assert(!p.owner_before(q) && !q.owner_before(p)); // p and q share ownership
}
end example
]
namespace std {
  template<class T> class enable_shared_from_this {
  protected:
    constexpr enable_shared_from_this() noexcept;
    enable_shared_from_this(const enable_shared_from_this&) noexcept;
    enable_shared_from_this& operator=(const enable_shared_from_this&) noexcept;
    ~enable_shared_from_this();

  public:
    shared_ptr<T> shared_from_this();
    shared_ptr<T const> shared_from_this() const;
    weak_ptr<T> weak_from_this() noexcept;
    weak_ptr<T const> weak_from_this() const noexcept;

  private:
    mutable weak_ptr<T> weak_this;  // exposition only
  };
}
The template parameter T of enable_­shared_­from_­this may be an incomplete type.
constexpr enable_shared_from_this() noexcept; enable_shared_from_this(const enable_shared_from_this<T>&) noexcept;
Effects: Value-initializes weak_­this.
enable_shared_from_this<T>& operator=(const enable_shared_from_this<T>&) noexcept;
Returns: *this.
[Note
:
weak_­this is not changed.
end note
]
shared_ptr<T> shared_from_this(); shared_ptr<T const> shared_from_this() const;
Returns: shared_­ptr<T>(weak_­this).
weak_ptr<T> weak_from_this() noexcept; weak_ptr<T const> weak_from_this() const noexcept;
Returns: weak_­this.