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2876. shared_ptr::shared_ptr(const weak_ptr<Y>&) constructor should be constrained

Section: 20.3.2.2.2 [util.smartptr.shared.const] Status: C++17 Submitter: United States Opened: 2017-02-03 Last modified: 2020-09-06

Priority: Not Prioritized

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Discussion:

Addresses US 129

Paragraph 22: This constructor should not participate in overload resolution unless the requirements are satisfied, in order to give correct results from the is_constructible trait.

Proposed change:

Add a Remarks: clause to constrain this constructor not to participate in overload resolution unless the Requires clause is satisfied.

[2017-02-23, Jonathan provides wording]

[Kona 2017-02-27]

Accepted as Immediate to resolve NB comment.

Proposed resolution:

This wording is relative to N4640.

1. Modify 20.3.2.2.2 [util.smartptr.shared.const] as indicated:

   template<class Y> explicit shared_ptr(const weak_ptr<Y>& r);
   

   -22- Requires: Y* shall be compatible with T*.

   […]

   -25- Throws: […]

   -?- Remarks: This constructor shall not participate in overload resolution unless Y* is compatible with T*.