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

Section: 20.11.3.2 [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 20.11.3.2 [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*`.