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915. minmax with initializer_list should return pair of T, not pair of const T&

Section: 27.8.9 [alg.min.max] Status: NAD Editorial Submitter: Daniel Krügler Opened: 2008-10-04 Last modified: 2016-01-28

Priority: Not Prioritized

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Discussion:

It seems that the proposed changes for N2772 were not clear enough in this point:

27.8.9 [alg.min.max], before p.23 + p.24 + before p. 27 + p. 28 say that the return type of the minmax overloads with an initializer_list is pair<const T&, const T&>, which is inconsistent with the decision for the other min/max overloads which take a initializer_list as argument and return a T, not a const T&. Doing otherwise for minmax would easily lead to unexpected life-time problems by using minmax instead of min and max separately.

[ Batavia (2009-05): ]

We agree with the proposed resolution. Move to Tentatively Ready.

[ 2009-07 Frankfurt ]

Moved from Tentatively Ready to Open only because the wording needs to be tweaked for concepts removal.

[ 2009-08-18 Daniel adds: ]

Recommend NAD since the proposed changes have already been performed as part of editorial work of N2914.

[ 2009-10 Santa Cruz: ]

Can't find initializer_list form of minmax anymore, only variadic version. Seems like we had an editing clash with concepts. Leave Open, at least until editorial issues resolved. Bring this to Editor's attention.

[ 2010 Pittsburgh: Pete to reapply N2772. ]

Rationale:

Solved by reapplying N2772.

Proposed resolution:

1. In 27 [algorithms]/2, header <algorithm> synopsis change as indicated:

   template<classLessThanComparable T>
   requires CopyConstructible<T>
   pair<const T&, const T&>
   minmax(initializer_list<T> t);
   
   template<class T, classStrictWeakOrder<auto, T> Compare>
   requires CopyConstructible<T>
   pair<const T&, const T&>
   minmax(initializer_list<T> t, Compare comp);
   

2. In 27.8.9 [alg.min.max] change as indicated (Begin: Just before p.20):

   template<classLessThanComparable T>
     requires CopyConstructible<T>
     pair<const T&, const T&>
     minmax(initializer_list<T> t);
   

   -20- Requires: T is LessThanComparable and CopyConstructible.

   -21- Returns: pair<const T&, const T&>(x, y) where x is the smallest value and y the largest value in the initializer_list.

   [..]

   template<class T, classStrictWeakOrder<auto, T> Compare>
     requires CopyConstructible<T>
     pair<const T&, const T&>
     minmax(initializer_list<T> t, Compare comp);
   

   -24- Requires: type T is LessThanComparable and CopyConstructible.

   -25- Returns: pair<const T&, const T&>(x, y) where x is the smallest value and y largest value in the initializer_list.