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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: New Submitter: Jiang An Opened: 2023-12-16 Last modified: 2024-03-11

Priority: 2

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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.

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. […]