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4024. Underspecified destruction of objects created in std::make_shared_for_overwrite/std::allocate_shared_for_overwrite

Section: 20.3.2.2.7 [util.smartptr.shared.create] Status: WP Submitter: Jiang An Opened: 2023-12-16 Last modified: 2024-11-28

Priority: 2

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

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Discussion:

Currently, only destructions of non-array (sub)objects created in std::make_shared and std::allocate_shared are specified in 20.3.2.2.7 [util.smartptr.shared.create]. Presumably, objects created in std::make_shared_for_overwrite and std::allocate_shared_for_overwrite should be destroyed by plain destructor calls.

[2024-03-11; Reflector poll]

Set priority to 2 after reflector poll in December 2023.

This was the P1020R1 author's intent (see LWG reflector mail in November 2018) but it was never clarified in the wording. This fixes that.

[2024-08-21; Move to Ready at LWG telecon]

[Wrocław 2024-11-23; Status changed: Voting → WP.]

Proposed resolution:

This wording is relative to N4964.

1. Modify 20.3.2.2.7 [util.smartptr.shared.create] as indicated:

   template<class T, ...>
     shared_ptr<T> make_shared(args);
   template<class T, class A, ...>
     shared_ptr<T> allocate_shared(const A& a, args);
   template<class T, ...>
     shared_ptr<T> make_shared_for_overwrite(args);
   template<class T, class A, ...>
     shared_ptr<T> allocate_shared_for_overwrite(const A& a, args);
   

   […]

   -7- Remarks:

   1. […]

   2. (7.11) — When a (sub)object of non-array type U that was initialized by make_shared, make_shared_for_overwrite, or allocate_shared_for_overwrite is to be destroyed, it is destroyed via the expression pv->~U() where pv points to that object of type U.

   3. […]