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2873. Add noexcept to several shared_ptr related functions

Section: 20.3.2.2 [util.smartptr.shared] 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 124

Several shared_ptr related functions have wide contracts and cannot throw, so should be marked unconditionally noexcept.

Proposed change:

Add noexcept to: 

template<class U> 
bool 
shared_ptr::owner_before(shared_ptr<U> const& b) const noexcept;
 
template<class U> 
bool 
shared_ptr::owner_before(weak_ptr<U> const& b) const noexcept;

template<class U> 
bool  
weak_ptr::owner_before(shared_ptr<U> const& b) const noexcept; 

template<class U> 
bool
weak_ptr::owner_before(weak_ptr<U> const& b) const noexcept;
 
bool owner_less::operator()(A,B) const noexcept; // all versions

[2017-02-20, Marshall adds 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 [util.smartptr.shared] as indicated:

      template<class U> bool owner_before(const shared_ptr<U>& b) const noexcept;
  template<class U> bool owner_before(const weak_ptr<U>& b) const noexcept;

  2. Modify 20.3.2.2.6 [util.smartptr.shared.obs] as indicated: 

    template<class U> bool owner_before(const shared_ptr<U>& b) const noexcept;
template<class U> bool owner_before(const weak_ptr<U>& b) const noexcept;

  3. Modify 20.3.2.4 [util.smartptr.ownerless] as indicated:

    template<class T> struct owner_less<shared_ptr<T>> {
   bool operator()(const shared_ptr<T>&, const shared_ptr<T>&) const noexcept;
   bool operator()(const shared_ptr<T>&, const weak_ptr<T>&) const noexcept;
   bool operator()(const weak_ptr<T>&, const shared_ptr<T>&) const noexcept;
};

template<class T> struct owner_less<weak_ptr<T>> {
   bool operator()(const weak_ptr<T>&, const weak_ptr<T>&) const noexcept;
   bool operator()(const shared_ptr<T>&, const weak_ptr<T>&) const noexcept;
   bool operator()(const weak_ptr<T>&, const shared_ptr<T>&) const noexcept;
};

template<> struct owner_less<void> {
   template<class T, class U>
      bool operator()(const shared_ptr<T>&, const shared_ptr<U>&) const noexcept;
   template<class T, class U>
      bool operator()(const shared_ptr<T>&, const weak_ptr<U>&) const noexcept;
   template<class T, class U>
      bool operator()(const weak_ptr<T>&, const shared_ptr<U>&) const noexcept;
   template<class T, class U>
      bool operator()(const weak_ptr<T>&, const weak_ptr<U>&) const noexcept;
   using is_transparent = unspecified;
};