Issue 2495: There is no such thing as an Exception Safety element

This page is a snapshot from the LWG issues list, see the Library Active Issues List for more information and the meaning of C++17 status.

2495. There is no such thing as an Exception Safety element

Section: 20.3.2.2.2 [util.smartptr.shared.const] Status: C++17 Submitter: Jonathan Wakely Opened: 2015-05-05 Last modified: 2017-07-30

Priority: 0

View other active issues in [util.smartptr.shared.const].

View all other issues in [util.smartptr.shared.const].

View all issues with C++17 status.

Discussion:

20.3.2.2.2 [util.smartptr.shared.const] includes several "Exception safety" elements, but that is not one of the elements defined in 17.5.1.4 16.3.2.4 [structure.specifications]. We should either define what it means, or just move those sentences into the Effects: clause.

[2015-06, Telecon]

Move to Tentatively Ready.

Proposed resolution:

This wording is relative to N4431.

Change 20.3.2.2.2 [util.smartptr.shared.const] as follows:
```
template<class Y> explicit shared_ptr(Y* p);
```
[…]
-4- Effects: Constructs a shared_ptr object that owns the pointer p. If an exception is thrown, delete p is called.
[…]
~~-7- Exception safety: If an exception is thrown, delete p is called.~~
```
template <class Y, class D> shared_ptr(Y* p, D d);
template <class Y, class D, class A> shared_ptr(Y* p, D d, A a);
template <class D> shared_ptr(nullptr_t p, D d);
template <class D, class A> shared_ptr(nullptr_t p, D d, A a);
```
[…]
-9- Effects: Constructs a shared_ptr object that owns the object p and the deleter d. The second and fourth constructors shall use a copy of a to allocate memory for internal use. If an exception is thrown, d(p) is called.
[…]
~~-12- Exception safety: If an exception is thrown, d(p) is called.~~

[…]
```
template <class Y> explicit shared_ptr(const weak_ptr<Y>& r);
```
[…]
-24- Effects: Constructs a shared_ptr object that shares ownership with r and stores a copy of the pointer stored in r. If an exception is thrown, the constructor has no effect.
[…]
~~-27- Exception safety: If an exception is thrown, the constructor has no effect.~~
```
template <class Y, class D> shared_ptr(unique_ptr<Y, D>&& r);
```
[…]
-29- Effects: Equivalent to shared_ptr(r.release(), r.get_deleter()) when D is not a reference type, otherwise shared_ptr(r.release(), ref(r.get_deleter())). If an exception is thrown, the constructor has no effect.
~~-30- Exception safety: If an exception is thrown, the constructor has no effect.~~